Elise Da-Silva
email: elise.dasilva@orange.fr

Julia Baudart

Lise Barthelmebs

Biosensing platforms based on whole cell and nucleic acid detection for Vibrio bacteria analysis : a review

Keywords: Vibrio detection, strip tests, optical biosensors, electrochemical biosensors, sample preparation

Vibrio related illnesses are increasing worldwide in humans and marine animals. The detection of these bacteria is still mainly performed using traditional microbiological methods based on culture grown on differential agar media which are labor intensive, time consuming and unsuitable for in-field and high-throughput analysis. To overcome these limitations, biosensing platforms have emerged as promising alternative tools for rapid, sensitive, and real-time detection of Vibrio species in clinical, food and environmental samples. In this review, we will focus on strip test devices, and on optical and electrochemical biosensors developed for Vibrio analysis. Particular attention is given to sample preparation techniques.

Introduction

Due to the increased prevalence of well-known pathogens and the emergence of novel pathogenic microorganisms in aquatic sources, global incidence of water-borne diseases is currently rising. This phenomenon results from a combination of complex human factors including inadequate water supply, sanitation, and hygiene issues as well as the intensification of continental run-off discharging pathogens into coastal waters. Environmental factors such as climate changes and extreme weather events could also induce the persistence of pathogens in water sources [START_REF] Bruto | Vibrio crassostreae, a benign oyster colonizer turned into a pathogen after plasmid acquisition[END_REF].

Among emerging and reemerging infectious agents, Vibrio bacteria are widely distributed in coastal and estuarine environments where they are found as free-living cells and also closely associated with marine animals, plankton, algae or abiotic surfaces [START_REF] Grimes | What Genomic Sequence Information Has Revealed About Vibrio Ecology in the Ocean-A Review[END_REF].

At least twelve Vibrio species, including V. cholerae O1 and O139 serogroups, responsible for cholera outbreaks, and V. parahaemolyticus and V. vulnificus involved in seafood-borne infections, have been described as human pathogens [START_REF] Tantillo | Updated perspectives on emerging vibrios associated with human infections[END_REF]. Cholera disease remains a major threat to public health, especially in countries without improved sanitation facilities. According to the World Health Organization [START_REF]WHO Cholera surveillance and number of cases[END_REF], 1.3 to 4.0 million cholera cases, leading to 21 000 to 143 000 deaths, occur each year in the world. However, the global impact is still largely underestimated because the majority of cases is not reported [START_REF] Ali | Updated Global Burden of Cholera in Endemic Countries[END_REF]. Furthermore, in the last decades, an increase in human Vibrio infections has been observed worldwide, mainly in Africa and in Asia, but also in USA [START_REF] Covis | annual summaries on human Vibrio cases reported to CDC[END_REF]. As an example, the number of vibriosis excluding V. cholerae O1 and O139 serogroups, had regularly increased between 2007 and 2014 from 549 to 1252 in this country.

The most frequently reported species during this seven-year analysis was V. parahaemolyticus, isolated from 39 to 51% of patients, followed by V. alginolyticus and V. vulnificus isolated from 16 to 19% and 10 to 14% of the patients, respectively.

Several pathogenic Vibrio species are also involved in mass mortalities of marine animals, leading to important economic losses in aquaculture. This is well illustrated by V. anguillarum and V. salmonicida, two major pathogens involved in outbreaks in eel and salmon, respectively [START_REF] Austin | Bacterial Fish Pathogens, Disease of Farmed and Wild Fish[END_REF], by V. splendidus and V. aestuarianus associated with summer mortality events affecting oyster farming in Europe [START_REF] Garnier | Molecular and phenotypic characterization of Vibrio aestuarianus subsp. francensis subsp. nov., a pathogen of the oyster Crassostrea gigas[END_REF], and by V. harveyi and V. nigripulchritudo, the main infectious agents of farmed shrimps [START_REF] De La Peña | Luminescent vibrios associated with mortality in pond-cultured shrimp Penaeus monodon in the Philippines: species composition[END_REF][START_REF] Goarant | Summer Syndrome" in Litopenaeus stylirostris in New Caledonia: Pathology and epidemiology of the etiological agent, Vibrio nigripulchritudo[END_REF].

Traditionally, Vibrio detection in clinical, food and environmental samples is assessed by microbiological methods based on culture grown on differential agar media followed by colony counting and phenotypic identification of isolated strains. However, these approaches suffer from inherent and well-known drawbacks since they are time-consuming and require a delay of up to a week for species identification. Furthermore, it has been shown that Vibrio bacteria are able to modify their metabolic and enzymatic activities in response to environmental changes, inducing phenotypic and biochemical variabilities, and leading to a low efficiency of these approaches for an accurate identification [START_REF] Abbott | Misidentification of Unusual Aeromonas Species as Members of the Genus Vibrio: a Continuing Problem[END_REF][START_REF] Croci | and the Vibrio parahaemolyticus Working Group, Comparison of different biochemical and molecular methods for the identification of Vibrio parahaemolyticus[END_REF]. Culture-based methods also fail to detect cells induced, by environmental stresses, to enter a viable but-non culturable (VBNC) state [START_REF] Baffone | Retention of virulence in viable but non-culturable halophilic Vibrio spp[END_REF][START_REF] Binsztein | Viable but Nonculturable Vibrio cholerae O1 in the Aquatic Environment of Argentina[END_REF][START_REF] Wong | Induction of viable but nonculturable state in Vibrio parahaemolyticus and its susceptibility to environmental stresses[END_REF][START_REF] Coutard | mRNA detection by reverse transcription-PCR for monitoring viability and potential virulence in a pathogenic strain of Vibrio parahaemolyticus in viable but nonculturable state[END_REF][START_REF] Amel | Survival of Vibrio fluvialis in seawater under starvation conditions[END_REF].

It appears that the surveillance programs suffer from a lack of rapid and sensitive tools to detect pathogenic Vibrio strains in various matrix samples. In order to ensure relevant diagnosis, alternative methods to culture ones have to meet several criteria. Ideally, they must be accurate and reliable, rapid and low cost, automated or integrated into systems to provide highthroughput analysis. They should also be suitable for a broad range of applications and offer simultaneous detection of multiple targets.

During the last decades, biosensing platforms, mainly represented by biosensors, have been proposed as attractive and effective alternatives to detect microorganisms for clinical diagnosis, food analysis and environmental monitoring [START_REF] Nayak | Detection of microorganisms using biosensors -A smarter way towards detection techniques[END_REF][START_REF] Poltronieri | Biosensors for the Detection of Food Pathogens[END_REF][START_REF] Yoo | Optical Biosensors for the Detection of Pathogenic Microorganisms[END_REF].

Biosensors are analytical devices typically comprising (i) a bioreceptor (i.e., an antibody for lipopolysaccharide in the outer membrane, an aptamer selected to recognize the whole cell, a DNA sequence that is complementary to Vibrio DNA) which corresponds to the biological recognition element able to detect the target analyte and (ii) a transducer (i.e., optical, electrochemical, mechanical) that converts the biochemical reaction induced by the bio-recognition event into a measurable signal (Fig. 1). Compared to current diagnostic methods, biosensors offer several advantages since they are highly sensitive, low-cost, easy-touse and could allow real-time analysis. Optical and electrochemical transduction techniques More recently, the use of paper-based platforms, especially strip tests has also been intensively reported for Vibrio analysis. These devices are based on the analyte migration, under capillary action, through different zones of a membrane, on which bioreceptors (i.e., antibodies, aptamers, DNA probes) are immobilized. The analyte recognition leads to a response on the test line that can be assessed by eye or using a reader. A response on the control line validates the proper migration of the sample through the membrane (Fig. 2). Strip tests don't require laboratory infrastructure or technical expertise and thus, constitute interesting screening tools for a rapid analysis to be performed at the point of care (Cheng et al., 2014 ;Kim et al., 2015).

Thus, the purpose of this review is to examine the current status of biosensing platforms for Vibrio bacteria detection. In order to allow bacteria sensing, two main strategies can be considered: the direct detection of whole bacterial cells or the detection of specific nucleic acid targets after the bacterial lysis. Toxin detection is not addressed in this article. For each of these strategies, strip tests, and biosensors either optical or electrochemical, targeting Vibrio are presented. A special emphasis is placed on sample preparation techniques used prior analysis.

Further, current trends, advantages and disadvantages and future prospects of these methods are discussed.

Sample preparation before analysis

Due to their influence on the performance of the analytical methods for bacteria determination, techniques applied to sample preparation are of great importance.

Depending on the bioreceptor, biosensors and strip tests designed for bacteria analysis are able to detect either whole cells, using antibodies or aptamers, or nucleic acids, using complementary DNA sequences as probes. Furthermore, these tools are, in principle, dedicated to real sample analysis. Thus, sample preparation has to be adapted not only to the type of biosensor but also to the kind of sample. In the case of Vibrio monitoring, commonly analyzed matrices are food (shrimps, oysters, mussels, clams), clinical (stool and blood), and environmental samples (seawater, ground water, tap water). Since these complex matrices could contain some compounds interfering with the response signal, such as fats, polysaccharides, proteins, minerals and even some antimicrobial preservatives, a preliminary treatment step is generally needed prior analysis. Besides, Vibrio cells are usually present at low levels in environmental samples such as water, requiring the use of concentration techniques to allow their detection and avoid false negative results. The different sample preparation methods reported in the literature for Vibrio analysis by biosensor and strip test technologies are detailed below.

Whole cell preparation

To validate the biosensing tools targeting whole cells, Vibrio strains are cultivated in an appropriate medium, the cells are then harvested by centrifugation, washed and resuspended at different concentrations in saline buffer or nutritive medium. The obtained suspensions are then directly used for analysis [START_REF] Thattiyaphong | Development of a 5-minute rapid test for detecting Vibrio cholerae O139, Southeast Asian[END_REF][START_REF] Pengsuk | Development and evaluation of a highly sensitive immunochromatographic strip test using gold nanoparticle for direct detection of Vibrio cholerae O139 in seafoodsamples[END_REF][START_REF] Zhao | Upconversion fluorescent strip sensor for rapid determination of Vibrio anguillarum[END_REF][START_REF] Wu | Colorimetric Aptasensor Based on Enzyme for the Detection of Vibrio parahemolyticus[END_REF][START_REF] Duan | Vibrio parahaemolyticus detection aptasensor using surface-enhanced Raman scattering[END_REF][START_REF] Liu | Development of a highly sensitive lateral immunochromatographic assay for rapid detection of Vibrio parahaemolyticus[END_REF] or added to real samples, often pretreated, to evaluate their matrix effect. Liquid samples, such as water, are usually sterilized by a filtration through 0.2 or 0.45 µm pore size membranes [START_REF] Wu | Colorimetric Aptasensor Based on Enzyme for the Detection of Vibrio parahemolyticus[END_REF][START_REF] Duan | Vibrio parahaemolyticus detection aptasensor using surface-enhanced Raman scattering[END_REF]. For solid samples, such as seafood, a mass of product is mixed and homogenized in buffer or in alkaline peptone (APW) [START_REF] Pengsuk | Development and evaluation of a highly sensitive immunochromatographic strip test using gold nanoparticle for direct detection of Vibrio cholerae O139 in seafoodsamples[END_REF][START_REF] Park | Sensitive immunoassay-based detection of Vibrio parahaemolyticus using capture and labeling particles in a stationary liquid phase lab-on-a-chip[END_REF]. A filtration step can be added to remove the large debris [START_REF] Duan | Vibrio parahaemolyticus detection aptasensor using surface-enhanced Raman scattering[END_REF][START_REF] Liu | Facile synthesis of multifunctional multi-walled carbon nanotube for pathogen Vibrio alginolyticus detection in fishery and environmental samples[END_REF][START_REF] Duan | A universal fluorescent aptasensor based on AccuBlue dye for the detection of pathogenic bacteria[END_REF].

Similar protocols are applied to Vibrio cells from naturally contaminated samples, which are, in most of cases, stools from patients presenting cholera symptoms. After a simple dilution step in appropriate buffer, liquid stool samples are usually directly analyzed [START_REF] Kalluri | Evaluation of three rapid diagnostic tests for cholera: does the skill level of the technician matter?[END_REF][START_REF] Harris | Field evaluation of Crystal VC ® Rapid Dipstick test for cholera during a cholera outbreak in Guinea-Bissau: Evaluation of a rapid test for cholera[END_REF][START_REF] Mukherjee | Evaluation of a rapid immunochromatographic dipstick kit for diagnosis of cholera emphasizes its outbreak utility[END_REF][START_REF] Sinha | Evaluation of a rapid dipstick test for identifying cholera cases during the outbreak[END_REF][START_REF] Page | Evaluation of a Rapid Test for the Diagnosis of Cholera in the Absence of a Gold Standard[END_REF][START_REF] George | Evaluation of enrichment method for the detection of Vibrio cholerae O1 using a rapid dipstick test in Bangladesh[END_REF]. A pre-enrichment step can also be carried out in APW for 4 to 6h at an appropriate growth temperature to increase the bacterial biomass [START_REF] George | Evaluation of enrichment method for the detection of Vibrio cholerae O1 using a rapid dipstick test in Bangladesh[END_REF][START_REF] Bhuiyan | Use of Dipsticks for Rapid Diagnosis of Cholera Caused by Vibrio cholerae O1 and O139 from Rectal Swabs[END_REF][START_REF] Ontweka | Cholera Rapid Test with Enrichment Step Has Diagnostic Performance Equivalent to Culture[END_REF]. In order to determine the concentration of cells, and/or to check the presence of Vibrio in samples, culturable cells are always enumerated in parallel by classical culture-based methods.

Nucleic acid preparation

Nucleic acid extraction is a critical step to obtain a positive signal in biosensor analysis. The selected method must allow to obtain pure and concentrated nucleic acid extracts. Among the numerous methods available for this purpose, the boiling lysis method is mainly used for DNA extraction from pure culture [START_REF] Yean | Enzyme-Linked Amperometric Electrochemical Genosensor Assay for the Detection of PCR Amplicons on a Streptavidin-Treated Screen-Printed Carbon Electrode[END_REF][START_REF] Low | Electrochemical genosensor for specific detection of the food-borne pathogen, Vibrio cholerae[END_REF][START_REF] Yu | Enzymatic electrochemical detection of epidemic-causing Vibrio cholerae with a disposable oligonucleotide-modified screen-printed bisensor coupled to a dry-reagent-based nucleic acid amplification assay[END_REF][START_REF] Xu | A cross-priming amplification assay coupled with vertical flow visualization for detection of Vibrio parahaemolyticus[END_REF]. Cells are boiled for 10 min in saline solution, the lysate is centrifuged and the released DNA is recovered from the supernatant. Commercial DNA extraction kits such as QIAamp® DNA minikit from Qiagen, and Nucleospin® Tissue from Macherey-Nagel, are also used to extract and purify DNA from pure cultures in 30 to 45 minutes with a high-throughput [START_REF] Surasilp | Rapid and sensitive detection of Vibrio vulnificus by loop-mediated isothermal amplification combined with lateral flow dipstick targeted to rpoS gene[END_REF][START_REF] Plaon | Rapid and Sensitive Detection of Vibrio alginolyticus by Loop-Mediated Isothermal Amplification Combined with a Lateral Flow Dipstick Targeted to the rpoX Gene[END_REF][START_REF] Liew | Electrochemical genosensor assay using lyophilized gold nanoparticles/latex microsphere label for detection of Vibrio cholerae[END_REF].

In the case of nucleic acids extraction from real samples, the boiling lysis method can also be applied [START_REF] Ang | Development of a dryreagent-based nucleic acid-sensing platform by coupling thermostabilised LATE-PCR assay to an oligonucleotide-modified lateral flow biosensor[END_REF][START_REF] Low | An Electrochemical Genosensing Assay Based on Magnetic Beads and Gold Nanoparticle-Loaded Latex Microspheres for Vibrio cholerae Detection[END_REF][START_REF] Low | A signal-amplified electrochemical DNA biosensor incorporated with a colorimetric internal control for Vibrio cholerae detection using shelfready reagents[END_REF], with slight modifications such as the addition of a chemical lysis before boiling for shrimp and oyster samples [START_REF] Surasilp | Rapid and sensitive detection of Vibrio vulnificus by loop-mediated isothermal amplification combined with lateral flow dipstick targeted to rpoS gene[END_REF][START_REF] Plaon | Rapid and Sensitive Detection of Vibrio alginolyticus by Loop-Mediated Isothermal Amplification Combined with a Lateral Flow Dipstick Targeted to the rpoX Gene[END_REF][START_REF] Prompamorn | The development of loop-mediated isothermal amplification combined with lateral flow dipstick for detection of Vibrio parahaemolyticus[END_REF][START_REF] Thongkao | Rapid and sensitive detection of Vibrio harveyi by loop-mediated isothermal amplification combined with lateral flow dipstick targeted to vhhP2 gene[END_REF]. Nucleic acids can also be extracted using the phenol chloroform method, in order to complex and eliminate polysaccharides from the samples [START_REF] Patel | A Label-Free Photoluminescence Genosensor Using Nanostructured Magnesium Oxide for Cholera Detection[END_REF][START_REF] Da-Silva | Development of a PCR-free DNA-based assay for the specific detection of Vibrio species in environmental samples by targeting the 16S rRNA[END_REF]. Nevertheless, this method is laborious and uses toxic compounds. As a good alternative to those methods, several companies have developed kits to decrease extraction time and to obtain nucleic acids without inhibitors. Surprisingly, no publication concerning Vibrio detection using biosensing platforms has reported the use of such kits.

Recently, an automated method was reported for DNA extraction from pure cultures and spiked tap water samples. This step is incorporated into a rotary microfluidic system, using glass microbeads as solid phase matrix allowing a strong DNA adsorption in presence of chaotropic salts [START_REF] Park | An integrated rotary microfluidic system with DNA extraction, loop-mediated isothermal amplification, and lateral flow strip based detection for point-of-care pathogen diagnostics[END_REF].

After DNA extraction, direct quantification of the extracted nucleic acids is rarely performed since the majority of the assays used an amplification step of DNA by PCR before analysis.

The obtained PCR products are often subjected to gel electrophoresis for quality checking [START_REF] Yean | Enzyme-Linked Amperometric Electrochemical Genosensor Assay for the Detection of PCR Amplicons on a Streptavidin-Treated Screen-Printed Carbon Electrode[END_REF][START_REF] Low | Electrochemical genosensor for specific detection of the food-borne pathogen, Vibrio cholerae[END_REF] and their concentration is measured by spectrophotometry at 260 nm [START_REF] Liew | Electrochemical genosensor assay using lyophilized gold nanoparticles/latex microsphere label for detection of Vibrio cholerae[END_REF]. The doublestranded PCR products can be denatured by a heating step at 95°C during few minutes, sometimes followed by a cooling step on ice to obtain single stranded-DNA (ssDNA) for the hybridization reaction with DNA probes [START_REF] Ang | Development of a dryreagent-based nucleic acid-sensing platform by coupling thermostabilised LATE-PCR assay to an oligonucleotide-modified lateral flow biosensor[END_REF]. An asymmetric PCR, or a linear after the exponential PCR (LATE-PCR), can also be applied to directly generate ssDNA amplicons [START_REF] Low | Electrochemical genosensor for specific detection of the food-borne pathogen, Vibrio cholerae[END_REF][START_REF] Surasilp | Rapid and sensitive detection of Vibrio vulnificus by loop-mediated isothermal amplification combined with lateral flow dipstick targeted to rpoS gene[END_REF][START_REF] Ang | Development of a dryreagent-based nucleic acid-sensing platform by coupling thermostabilised LATE-PCR assay to an oligonucleotide-modified lateral flow biosensor[END_REF][START_REF] Yu | Multiplex electrochemical genosensor for identifying toxigenic Vibrio cholerae serogroups O1 and O139[END_REF].

Interestingly, in some recent reports, direct nucleic acid detection was performed without any amplification step by PCR. Nucleic acid concentration, purity and integrity were assessed using either Nanodrop spectrophotometer [START_REF] Patel | Biocompatible nanostructured magnesium oxide-chitosan platform for genosensing application[END_REF][START_REF] Patel | Magnesium oxide grafted carbon nanotubes based impedimetric genosensor for biomedical application[END_REF][START_REF] Narmani | Highly sensitive and accurate detection of Vibrio cholera O1 OmpW gene by fluorescence DNA biosensor based on gold and magnetic nanoparticles[END_REF], Eppendorf Biophotometer [START_REF] Nordin | A simple, portable, electrochemical biosensor to screen shellfish for Vibrio parahaemolyticus[END_REF], or Agilent 2100 Bioanalyzer [START_REF] Da-Silva | Development of a PCR-free DNA-based assay for the specific detection of Vibrio species in environmental samples by targeting the 16S rRNA[END_REF]. Prior to biosensor analysis, a pretreament step was nevertheless needed to improve the recognition between probes and targets. For DNA samples, this pretreatment consisted in a denaturation at 92°C for few minutes immediately followed by an ice cooling [START_REF] Nordin | A simple, portable, electrochemical biosensor to screen shellfish for Vibrio parahaemolyticus[END_REF]. The heating step could also be combined with an ultrasonication fragmentation [START_REF] Patel | Biocompatible nanostructured magnesium oxide-chitosan platform for genosensing application[END_REF][START_REF] Patel | Magnesium oxide grafted carbon nanotubes based impedimetric genosensor for biomedical application[END_REF]. For RNA samples, a chemical fragmentation step was applied [START_REF] Da-Silva | Development of a PCR-free DNA-based assay for the specific detection of Vibrio species in environmental samples by targeting the 16S rRNA[END_REF].

Biosensing platforms for the detection of whole bacterial cells

One of the most important factors in the set-up of biosensing platforms for whole bacterial cells is to define a suitable targeted molecule linked to the bacterial cell surface, such as outer membrane lipopolysaccharide, a virulence factor in pathogenic Vibrio species. This targeted molecule is then used to produce specific bioreceptors (i.e., antibodies, aptamers), which will be integrated into biosensing platforms to allow a direct and rapid detection of bacteria with high affinity and specificity.

Strip test devices

The strip tests developed for the detection of whole Vibrio cells are summarized in Table 1.

All these devices are based on a lateral flow immunochromatography assay (LFA) using antibodies as presented in Fig. 2.

Since cholera mainly affects developing countries with poor resources and limited access to laboratory facilities, strip test devices appear as interesting tools to detect this disease. Thus, numerous strip tests have been developed for the detection of V. cholerae species in stool samples (Table 1). The most widely used is the Pasteur Institut dipstick, nowadays commercially available as Crystal VC ® RDT (Span Diagnostics Ltd., India). This test is able to detect the lipopolysaccharide (LPS) antigen of V. cholerae O1 and O139 using specific monoclonal antibodies (MAb) in about 10 min. Several studies have evaluated the performances of both the prototype and the commercial version. Most of these studies used culture on solid medium as reference method. The sensitivity corresponds to the proportion of patients with positive strip tests among patients diagnosed positive by a reference method whereas the specificity corresponds to the proportion of patients with negative strip tests among patients diagnosed negative by a reference method. A first evaluation on frozen stool samples showed high sensitivity and specificity ranging from 94.2 to 100% and from 84 to 100%, respectively [START_REF] Nato | One-Step Immunochromatographic Dipstick Tests for Rapid Detection of Vibrio cholerae O1 and O139 in Stool Samples[END_REF]. These observations were in accordance with the results obtained for rectal swab analysis with sensitivity and specificity ranging from 93-96% and 92-98%, respectively [START_REF] Bhuiyan | Use of Dipsticks for Rapid Diagnosis of Cholera Caused by Vibrio cholerae O1 and O139 from Rectal Swabs[END_REF]. However, two studies performed on bulk stools during cholera outbreaks showed lower specificities ranging from 71% to 77% and from 77% to 97% [START_REF] Harris | Field evaluation of Crystal VC ® Rapid Dipstick test for cholera during a cholera outbreak in Guinea-Bissau: Evaluation of a rapid test for cholera[END_REF][START_REF] Wang | Field evaluation of a rapid immunochromatographic dipstick test for the diagnosis of cholera in a high-risk population[END_REF]. In order to increase the sensitivity of the assay and to obtain performances similar to that of culture [START_REF] Ontweka | Cholera Rapid Test with Enrichment Step Has Diagnostic Performance Equivalent to Culture[END_REF], an enrichment of samples in APW was often performed prior analysis. Recent studies have shown that a 24h enrichment step in APW significantly increased the sensitivity compared to a direct testing [START_REF] Chakraborty | Adaptation of a simple dipstick test for detection of Vibrio cholerae O1 and O139 in environmental water[END_REF] whereas after 6h of enrichment, the sensitivity was only marginally increased [START_REF] George | Evaluation of enrichment method for the detection of Vibrio cholerae O1 using a rapid dipstick test in Bangladesh[END_REF]. The importance of the reference method was also underlined by several reports [START_REF] Mukherjee | Evaluation of a rapid immunochromatographic dipstick kit for diagnosis of cholera emphasizes its outbreak utility[END_REF][START_REF] Page | Evaluation of a Rapid Test for the Diagnosis of Cholera in the Absence of a Gold Standard[END_REF] since a significant increase in the assay specificity was observed when both culture and PCR were used as references. Some authors have also highlighted the impact of the technician skill level on the test specificity [START_REF] Kalluri | Evaluation of three rapid diagnostic tests for cholera: does the skill level of the technician matter?[END_REF][START_REF] Ley | Evaluation of a Rapid Dipstick (Crystal VC) for the Diagnosis of Cholera in Zanzibar and a Comparison with Previous Studies[END_REF] that can vary, for example, from 67% when the assay was performed by field paramedics to 76% when the users were lab technicians [START_REF] Kalluri | Evaluation of three rapid diagnostic tests for cholera: does the skill level of the technician matter?[END_REF].

Strip test devices were also proposed for the rapid and specific detection of Vibrio cholerae O1 serotype Ogawa [START_REF] Chen | Development of an immunochromatographic lateral flow device for rapid diagnosis of Vibrio cholerae O1 serotype Ogawa[END_REF]. The test was based on a LFA using MAb highly specific to the Ogawa serotype and colloidal gold particles-antibodies conjugates. The limit of detection (LOD) of the developed device was 10 4 CFU mL -1 and showed 100% sensitivity and selectivity compared to standard culture method. Others LFAs, were developed for the detection of V. cholerae O139 alone. These tools showed sensitivities ranging from 10 4 [START_REF] Pengsuk | Development and evaluation of a highly sensitive immunochromatographic strip test using gold nanoparticle for direct detection of Vibrio cholerae O139 in seafoodsamples[END_REF] to 10 6 CFU mL -1 [START_REF] Thattiyaphong | Development of a 5-minute rapid test for detecting Vibrio cholerae O139, Southeast Asian[END_REF] and were highly specific. Although strip tests can be used for early detection of cholera, all those studies reveal some limitations since the tools can fail to detect V. cholerae leading to false negative results [START_REF] Mukherjee | Evaluation of a rapid immunochromatographic dipstick kit for diagnosis of cholera emphasizes its outbreak utility[END_REF][START_REF] Sinha | Evaluation of a rapid dipstick test for identifying cholera cases during the outbreak[END_REF][START_REF] Nato | One-Step Immunochromatographic Dipstick Tests for Rapid Detection of Vibrio cholerae O1 and O139 in Stool Samples[END_REF].

More recently, two similar assays have been described for the detection of other Vibrio species. The first one, targeting V. parahaemolyticus, showed an LOD of 1.2 x 10 3 CFU mL -1 using pure cultures and no cross reaction within a panel of 32 species [START_REF] Liu | Development of a highly sensitive lateral immunochromatographic assay for rapid detection of Vibrio parahaemolyticus[END_REF]. Furthermore, when performed on hepatopancreas and fecal samples from shrimp, and on human fecal samples, the assay demonstrated 100% sensitivity and specificity. In the second one, specifically designed for V. anguillarum detection, the sensitivity of the assay was increased using upconversion fluorescent materials, able to convert near infrared light into visible light, instead of standard gold nanoparticles reporters [START_REF] Zhao | Upconversion fluorescent strip sensor for rapid determination of Vibrio anguillarum[END_REF]. This assay demonstrated an LOD of 10 2 CFU mL -1 and no cross-reaction with 8 other pathogenic species (V. alginolyticus, V. harveyi, V. parahaemolyticus, V. vulnificus, Escherichia coli, Edwardsiella tarda, Streptococcus iniae, and Staphylococcus aureus).

Optical biosensors

Comparatively to LFA, few optical immunosensors were proposed for the detection of whole Vibrio cells as reported in Table 2.

The first optical immunosensor was applied to V. cholerae detection and was based on surface plasmon resonance (SPR) detection technique. A detection range of 10 5 -10 9 cells mL -1 and an LOD of 10 5 cells mL -1 were obtained using MAb against LPS as bioreceptors [START_REF] Jyoung | Immunosensor for the detection of Vibrio cholerae O1 using surface plasmon resonance[END_REF]. An interesting study showed that, by targeting the outer membrane protein OmpW instead of the LPS, linear range and LOD were significantly improved to 10 2 -10 5 cells mL -1 and 43 cells mL - 1 , respectively [START_REF] Taheri | Development of an immunosensor using oriented immobilized anti-OmpW for sensitive detection of Vibrio cholerae by surface plasmon resonance[END_REF].

An immunosensor with 1-pyrenebutyric acid as a fluorescent reporter system grafted onto multi-walled carbon nanotubes (MWCNT) was developed to target V. alginolyticus [START_REF] Liu | Facile synthesis of multifunctional multi-walled carbon nanotube for pathogen Vibrio alginolyticus detection in fishery and environmental samples[END_REF]. The fluorescence intensity was correlated with culturable cell concentrations in the range 9.0 x 10 2 to 1.5 x 10 6 CFU mL -1 and the LOD was 2.8 x 10 2 CFU mL -1 when tested with pure bacterial culture. The sensor showed no cross reaction with the 4 other tested bacterial species (E. coli, Pseudomonas aeruginosa, S. aureus and Bacillus subtilis) and demonstrated recovery rates in the range of 89.4-94% and 95.9-102.3% when tested with shrimp and fishpond water samples, respectively.

A stationary liquid phase lab-on-chip (SLP-LOC) was recently described for V.

parahaemolyticus detection [START_REF] Park | Sensitive immunoassay-based detection of Vibrio parahaemolyticus using capture and labeling particles in a stationary liquid phase lab-on-a-chip[END_REF] (Fig. 3). The device is based on a sandwich immunoassay using magnetic nanoparticles (NP) functionalized with antibodies as capture particles and silica NP coated with horseradish peroxidase (HRP) and antibodies as labeling particles. V. parahaemolyticus was detected in the range 10 2 -10 6 CFU mL -1 with an LOD of 100 cells mL - 1 . The method was then successfully applied to the analysis of spiked oyster samples.

Alternatively to antibodies, aptamers constitute an interesting strategy for whole cell detection. These short oligonucleotides selected through an in vitro process (SELEX), are able to bind with high affinity and specificity to their target by a conformational change of their structure. Several aptamer-based assays were developed for V. parahaemolyticus detection.

The first assay, reported by Duan et al. [START_REF] Duan | A universal fluorescent aptasensor based on AccuBlue dye for the detection of pathogenic bacteria[END_REF], was based on a fluorescent "signal off" system.

The aptamers were first mixed with the targeted bacteria, followed by the addition of a complementary DNA (cDNA) and a sensitive fluorescent dsDNA dye (AccuBlue®). The hybridization occurring between free aptamers and cDNA formed a double-stranded DNA (dsDNA) revealed by the insertion of AccuBlue®, leading to the generation of a fluorescent signal. The linear dynamic range of detection was 50 to 10 6 CFU mL -1 with an LOD of 35 CFU mL -1 . No cross reaction with Salmonella typhimurium, S. aureus, E. coli and Listeria monocytogenes was observed. When tested with spiked shrimp samples, results were similar to those obtained with plate counting method showing the usefulness of the developed aptasensor for real sample analysis.

In a colorimetric assay, aptamers immobilized on magnetic NP were employed as capture probes whereas gold NPs coated with other aptamers and HRP were used as signal probes [START_REF] Wu | Colorimetric Aptasensor Based on Enzyme for the Detection of Vibrio parahemolyticus[END_REF].

The aptasensor responses were proportional to the target concentration in the range of 10-10 6 CFU mL -1 , with an LOD of 10 CFU mL -1 . No cross reactivity with other Vibrio and non-Vibrio strains was observed. The sensor validated with spiked water samples offered recoveries values between 92 and 102%.

An aptamer-based assay using surface-enhanced Raman scattering (SERS) detection technique was also developed [START_REF] Duan | Vibrio parahaemolyticus detection aptasensor using surface-enhanced Raman scattering[END_REF]. A first aptamer was immobilized on SiO2 functionalized with gold NP (SiO2@Au NPs) to capture the targeted bacteria. The captured cells were then revealed with a second aptamer conjugated to the Cyanine 3 fluorescent dye (Fig. 4). A linear relationship between the SERS signal and the target concentration was obtained in the same range as described above [START_REF] Wu | Colorimetric Aptasensor Based on Enzyme for the Detection of Vibrio parahemolyticus[END_REF], and with the same LOD. The developed sensor exhibited no cross reaction and good recovery rates ranging from 91 to 101% for spiked shrimp and water samples, respectively.

Electrochemical biosensors

The different electrochemical immunosensors reported for the detection of whole Vibrio cells are listed in Table 3. No electrochemical aptasensor has been published so far for Vibrio detection.

The first electrochemical biosensor has been developed by Rao et al. [65]. This tool was based on the indirect sandwich ELISA principle, with the use of polyclonal antibodies (PAb) directed towards the pathogen species V. cholerae, that were adsorbed on the surface of a screen printed electrode (SPE). Antibodies conjugated to alkaline phosphatase (ALP) were used as enzyme tracer to reveal the bacterial cell binding, and 1-naphtyl phosphate as the enzyme substrate, giving an electroactive product that can be detected via an amperometric measurement. The data showed that no cross reaction was observed with the 3 other Gram negative strains tested and that 10 5 cells mL -1 could be detected in only 55 minutes. This amperometric immunosensor was then applied to the analysis of spiked water samples detecting as few as 8 CFU mL -1 in seawater and 80 CFU mL -1 in tap water after an enrichment step [START_REF] Sharma | Immunological Biosensor for Detection of Vibrio cholerae O1 in Environmental Water Samples[END_REF].

A similar amperometric immunosensor allowing the detection of total Vibrio using a biotinylated PAb, immobilized on neutravidine modified surface of SPE was described [START_REF] Laczka | Application of an ELISA-type amperometric assay to the detection of Vibrio species with screen-printed electrodes[END_REF].

An LOD of 4.0 x 10 2 cells mL -1 was obtained without any enrichment step, in a total analytical time of 60 min.

Interestingly, two one-step label-free immunosensors were recently developed. The first one, designed for V. cholerae O1 detection, used antibodies covalently immobilized on a CeO2 nanowire-modified sensor surface of a microelectrode to capture the targets. The resulting complex was detected by impedance analysis with [Fe(CN)6] 3-/4-as the redox probe [START_REF] Tam | Label-free electrochemical immunosensor based on cerium oxide nanowires for Vibrio cholerae O1 detection[END_REF]. After optimization of experimental parameters an LOD of 1 x 10 2 CFU mL -1 was obtained. Specificity was only assessed with few strains (E. coli and Salmonella spp.). The second one targeting V. parahaemolyticus was applied to real samples [START_REF] Sha | A label-free multifunctionalized graphene oxide based electrochemiluminscence immunosensor for ultrasensitive and rapid detection of Vibrio parahaemolyticus in seawater and seafood[END_REF] (Fig. 5). The electrode surface was modified with a magnetic graphene oxide to immobilize antibodies, and an electrochemiluminescence detection was performed, using N-(4-aminobutyl)-N-ethylisoluminol as label, to detect the targeted cells. The proposed immunosensor exhibited ultrasensitive, specific and rapid detection of V. parahaemolyticus in seawater (LOD of 5 CFU mL -1 ), and in seafood (5 CFU g -1 ).

Biosensing platforms for nucleic acid detection

Nucleic acid detection is mainly based on the natural affinity of either ssDNA or RNA to its complementary strand, allowing to target specific genes. This strategy based on hybridization has been extensively assessed for DNA microarrays development in biotechnology and clinical diagnostics, and is nowadays transferred towards strip test devices and biosensors, referred as genosensors.

Strip test devices

Contrary to strip tests based on whole cell detection, mainly used for V. cholerae analysis, those based on nucleic acid detection have been developed for 5 well studied pathogen species of Vibrio (Table 4).

For all of these reported strip test devices, an amplification step is systematically applied on the extracted nucleic acids to generate DNA amplicons that were always labelled before analysis. As an example, lolB amplicons from V. cholerae were double tagged in 5' ends with biotin and fluorescein (FITC), and then captured on a glass-fiber membrane through biotin/streptavidin affinity [START_REF] Chua | A rapid DNA biosensor for the molecular diagnosis of infectious disease[END_REF]. The FITC was then recognized by anti-FITC antibodies coated with gold NPs to generate visual red lines. This LFA offered a detection sensitivity of 5 ng of PCR products, and a good specificity evaluated using 174 stool samples spiked with V. cholerae strains and other enteric bacteria.

In another study, the ctxA gene of V. cholerae was amplified by a LATE-PCR [START_REF] Ang | Development of a dryreagent-based nucleic acid-sensing platform by coupling thermostabilised LATE-PCR assay to an oligonucleotide-modified lateral flow biosensor[END_REF]. The amplicons were labeled with FITC and then bound to capture probes immobilized on the membrane. Hybridization revelation was performed using gold NPs coated with anti-FITC antibodies. This LFA showed sensitivities of 1 pg of pure genomic DNA and 10 CFU mL -1 of toxigenic V. cholerae. The biosensor demonstrated 100% specificity using spiked stool and a complete agreement with the results of the ELISA method.

Loop-mediated isothermal amplification (LAMP) coupled with a LFA using the rpoX gene as amplification target was described for V. alginolyticus detection [START_REF] Plaon | Rapid and Sensitive Detection of Vibrio alginolyticus by Loop-Mediated Isothermal Amplification Combined with a Lateral Flow Dipstick Targeted to the rpoX Gene[END_REF]. The biotinylated amplicons were first hybridized to a FITC labeled probe recognized by gold-conjugated anti-FITC antibodies. This complex was then captured on the membrane using streptavidin. LODs of the assay were 1.8 x 10 2 CFU mL -1 and 2 x 10 3 CFU g -1 for pure cultures and spiked shrimp samples, respectively. The same method coupling LAMP with LFA was applied to the detection of other Vibrio species. In pure culture, the LODs obtained for V. alginolyticus, V. parahaemolyticus [START_REF] Prompamorn | The development of loop-mediated isothermal amplification combined with lateral flow dipstick for detection of Vibrio parahaemolyticus[END_REF] and V. harveyi [START_REF] Thongkao | Rapid and sensitive detection of Vibrio harveyi by loop-mediated isothermal amplification combined with lateral flow dipstick targeted to vhhP2 gene[END_REF] were in the range of 10 2 CFU mL -1 , which was tenfold lower than that observed for V. vulnificus [START_REF] Surasilp | Rapid and sensitive detection of Vibrio vulnificus by loop-mediated isothermal amplification combined with lateral flow dipstick targeted to rpoS gene[END_REF]. A similar ratio between the LODs was also observed for real samples spiked with the same Vibrio strains.

In order to increase the sensitivity of the detection, an isothermal amplification technique, the cross-priming amplification, using multiple cross linked primers was combined with vertical flow assay to target the tlh gene of V. parahaemolyticus [START_REF] Xu | A cross-priming amplification assay coupled with vertical flow visualization for detection of Vibrio parahaemolyticus[END_REF]. Amplicons were doubled tagged with biotin and FITC, and hybridization was performed as described above, leading to very interesting LODs of 1.8 CFU mL -1 and 18 CFU g -1 for pure culture and spiked oyster samples, respectively. In another study, the toxR gene of V. parahaemolyticus was detected by using the same lateral flow principle coupled with a multiple cross displacement amplification, a novel isothermal amplification technique that yield amplicons as low as 3 bacterial cells [START_REF] Wang | Multiple Cross Displacement Amplification Combined with Gold Nanoparticle-Based Lateral Flow Biosensor for Detection of Vibrio parahaemolyticus[END_REF].

The test allowed the detection as low as 10 fg of DNA and 4.2 x 10 2 CFU mL -1 for pure cultures and spiked oyster samples, respectively. Among the 143 tested strains, no cross-reaction was observed with other Vibrio and non-Vibrio.

A more innovative procedure was proposed by Park et al. for V. parahaemolyticus detection, using an microfluidic system integrating DNA extraction, LAMP amplification and LFA [START_REF] Park | An integrated rotary microfluidic system with DNA extraction, loop-mediated isothermal amplification, and lateral flow strip based detection for point-of-care pathogen diagnostics[END_REF] (Fig. 6). Amplicons doubled-tagged with biotin and digoxygenin were immobilized on strips using anti-digoxygenin. Visual purple lines were obtained by addition of streptavidin coated gold NPs. The assay exhibited an LOD of 10 4 CFU mL -1 . By incorporating the extraction, amplification and detection steps in only one device, this rotary microfluidic system offers a rapid and a high-throughput analysis as well as multiplexing possibilities.

Optical biosensors

Few optical biosensors have been developed for the detection of nucleic acids from Vibrio species (Table 5). The first one, proposed by Lee et al. in 2003, was based on multiplex PCR followed by a colorimetric sandwich hybridization assay, allowing the simultaneous detection of V. vulnificus, V. cholerae, and V. parahaemolyticus [START_REF] Lee | Detection of pathogenic bacteria in shellfish using multiplex PCR followed by CovaLink TM NH microwell plate sandwich hybridization[END_REF]. After amplification, amplicons were hybridized between a phosphorylated capture probe immobilized on the surface of functionalized microplate and a biotinylated signal probe recognized by a ALP-avidin conjugate. When tested with oyster tissue homogenates, the assay allowed the detection as low as 10 2 CFU g -1 for each pathogen. These last years, other optical genosensors that did not require PCR amplification before nucleic acid analysis were developed. A label-free photoluminescent device, based on target DNA hybridization with complementary DNA probes coated onto nanostructured magnesium oxide NPs, was designed for V. cholerae detection [START_REF] Patel | A Label-Free Photoluminescence Genosensor Using Nanostructured Magnesium Oxide for Cholera Detection[END_REF]. Photoluminescence signal was proportional to the target DNA concentration in the range 100-500 ng µL -1 with an LOD of 3.133 ng µL -1 . More recently, the detection of V. cholerae ompW gene was achieved using a sandwich hybridization format device in which the target was recognized by both capture probes coated on magnetic NPs and FAM labeled probes immobilized on gold NPs [START_REF] Narmani | Highly sensitive and accurate detection of Vibrio cholera O1 OmpW gene by fluorescence DNA biosensor based on gold and magnetic nanoparticles[END_REF]. The reported device exhibited linear relationship between fluorescence emission and target DNA concentration in the range 10 to 250 ng mL -1 , with an LOD value of 2.34 ng mL -1 .

Due to its high copy number in prokaryote genomes, the presence of highly conserved regions and its a priori single stranded form, the rRNA molecule has been intensively used in genosensors for pathogen detection [START_REF] Tosar | Electrochemical DNA hybridization sensors applied to real and complex biological samples[END_REF]. However, only one study reported the detection of Vibrio using rRNA instead of DNA molecules [START_REF] Da-Silva | Development of a PCR-free DNA-based assay for the specific detection of Vibrio species in environmental samples by targeting the 16S rRNA[END_REF]. In this system, the target was bound between an immobilized capture probe and a labelled signal probe and hybridization event was revealed by chemiluminescence (Fig. 7). The described assay showed high specificity and an LOD of 5 ng µL -1 of RNA. Vibrio detection was achieved using pure cultures as well as spiked and real environmental samples. The study demonstrated that the microplates could be coated beforehand with capture probes and stored at 4°C for at least 1 month, in order to significantly reduce analysis time.

We could notice that the LOD values reported for these optical biosensors were not converted into CFU mL -1 which makes comparison with other methods difficult.

Electrochemical biosensors

The different electrochemical genosensors reported for the detection of nucleic acids from Vibrio bacteria are summarized in Table 6.

The first electrochemical genosensor was reported in 2008, and used amperometry for the detection of PCR amplicons from lolB gene of V. cholerae [START_REF] Yean | Enzyme-Linked Amperometric Electrochemical Genosensor Assay for the Detection of PCR Amplicons on a Streptavidin-Treated Screen-Printed Carbon Electrode[END_REF]. Amplicons were labelled both by biotin for the immobilization on streptavidin modified surface of a carbon SPE, and by fluorescein. They were then detected with HRP conjugated antifluorescein antibodies, followed by the addition of 3,3',5,5'-Tetramethylbenzidine and H2O2. The oxidation signal was analyzed using intermittent pulse amperometry, achieving an LOD of 10 CFU mL -1 of V. cholerae under the optimum conditions, and a good specificity. This system was then modified using asymmetric PCR to obtain ssDNA that could be integrated in a sandwich type hybridization strategy. This new format, associated with chrono-amperometry detection provided a good sensitivity (0.85 ng µL -1 ) and specificity of the analysis [START_REF] Low | Electrochemical genosensor for specific detection of the food-borne pathogen, Vibrio cholerae[END_REF].

Multiplex LATE-PCR assay was proposed to generate ssDNA amplicons from toxR gene that were integrated in an electrochemical genosensor also using a sandwich hybridization format. The complex was detected by an anti-FITC ALP conjugate that converts the substrate into electroactive α-naphtol, detected by amperometric measurement [START_REF] Yu | Multiplex electrochemical genosensor for identifying toxigenic Vibrio cholerae serogroups O1 and O139[END_REF]. Nucleic acids extracted from bacterial cultures and from spiked stools samples were used to validate the reported system. Two years later, the same research group has proposed a simplified version of this genosensor by developing a dry-reagent LATE PCR that just needs addition of DNA template and water to reconstitute the amplification mix, thus reducing the complexity of the assay [START_REF] Yu | Enzymatic electrochemical detection of epidemic-causing Vibrio cholerae with a disposable oligonucleotide-modified screen-printed bisensor coupled to a dry-reagent-based nucleic acid amplification assay[END_REF].

Interestingly, since 2013 magnetic beads and NPs were often included in the development of electrochemical genosensors for Vibrio detection. As an example, the use of streptavidin magnetic beads and antibody conjugated gold NPs was reported for the analysis of asymmetric PCR amplicons from V. cholerae lolB gene, in order to increase the surface area for bioreactions, and to label the complex, respectively [START_REF] Low | A thermostabilized magnetogenosensing assay for DNA sequence-specific detection and quantification of Vibrio cholerae[END_REF]. The new biosensor was successfully applied to the analysis of spiked stool samples, using differential pulse anodic stripping voltammetry (DPASV) for the electrochemical detection of the chemically dissolved gold NPs, leading to an LOD of 10 3 CFU mL -1 of V. cholerae. A new strategy, developed by the same authors, used gold NPs loaded onto a latex microsphere carrier to amplify the signal, and thus to improve the sensitivity of the assay [START_REF] Low | An Electrochemical Genosensing Assay Based on Magnetic Beads and Gold Nanoparticle-Loaded Latex Microspheres for Vibrio cholerae Detection[END_REF]. An LOD of 2 CFU mL -1 of V. cholerae in spiked stool samples was recorded using DPASV. Sensitivity of this approach was lower than that of other methods. Furthermore, an internal control was incorporated to this system to provide instant validation of the results, thus providing maximum diagnosis reliability. The new platform was validated with 38 reference bacterial strains, along with 145 clinical isolates, with a total assay time from sampling to measurement of less than 6h comprising 3h of enrichment step [START_REF] Low | A signal-amplified electrochemical DNA biosensor incorporated with a colorimetric internal control for Vibrio cholerae detection using shelfready reagents[END_REF]. In another work, gold NPs adsorbed on layer-by-layer modified latex were also integrated in a novel lyophilized reagent-based test. Measurements were performed following the same procedure as described above using either PCR or LAMP products for preliminary assays [START_REF] Liew | Electrochemical genosensor assay using lyophilized gold nanoparticles/latex microsphere label for detection of Vibrio cholerae[END_REF]. Interestingly, the lyophilized reagents were stable at room temperature for up to 1 month.

Two genosensors for the detection of V. cholerae O1 were proposed by the same research team using short fragments of genomic DNA, without the need of PCR amplification before analysis. These devices are both based on the use of nanostructured magnesium oxide for the electrode fabrication, either modified by chitosan [START_REF] Patel | Biocompatible nanostructured magnesium oxide-chitosan platform for genosensing application[END_REF], or grafted carboxyl functionalized MWCNT [START_REF] Patel | Magnesium oxide grafted carbon nanotubes based impedimetric genosensor for biomedical application[END_REF]. In the first method, DPV was applied to study the electrochemical response of methylene blue (MB), used as a redox probe to characterize the DNA complex formation. An LOD of 35.2 ng µL -1 of DNA was obtained, associated to a fast response time of 3 seconds [START_REF] Patel | Biocompatible nanostructured magnesium oxide-chitosan platform for genosensing application[END_REF]. In the second one, electrochemical impedance spectroscopy (EIS) was conducted with [Fe(CN)6] 3-/4-as redox probe, allowing a similar LOD of 21.7 ng µL -1 of DNA in 25 seconds [START_REF] Patel | Magnesium oxide grafted carbon nanotubes based impedimetric genosensor for biomedical application[END_REF]. Although these two genosensors showed interesting results with V. cholerae strains, their specificity was not tested with genomic DNA from other bacteria. Only interferences were assessed with glucose, cholesterol, ascorbic acid and sodium chloride.

Recently, a PCR-free electrochemical genosensor was adapted to the detection of V. parahaemolyticus, based on SPE modified with gold nanoparticles, and MB as the redox probe [START_REF] Nordin | A simple, portable, electrochemical biosensor to screen shellfish for Vibrio parahaemolyticus[END_REF] (Fig. 8). The hybridization reaction between the capture probe and the ssDNA molecule was recorded through DPV, with an LOD of 2.6 pM. The reported portable genosensor was successfully applied on spiked cockle samples. Another study reported the development of a PCR-free genosensor for V. cholerae detection using latex-gold NPs as DNA probe immobilization support in order to improve the sensitivity of the assay [START_REF] Rahman | Ultrasensitive Biosensor for the Detection of Vibrio cholerae DNA with Polystyrene-co-acrylic Acid Composite Nanospheres[END_REF]. The system was based on a sandwich hybridization format in which the target was bound between an immobilized capture probe and a signal probe. The hybridization event was monitored by DPV using an electroactive anthraquinone intercalator. The device allowed to detect as low as 1.0 x 10 21 M of complementary DNA and no cross reaction with Citrobacter freundii was observed.

However, the genosensor was not tested with real samples.

Conclusions

Vibrio detection still primarily relies on culture approach which take days to be completed.

The development of sensitive, specific and rapid tools to detect these bacteria in the environment remains challenging. These last years, biosensors and strip tests have been proposed to meet these criteria. Compared to culture method, these tools allow to significantly reduce the assay time (from days to hours) and to detect the viable but non culturable microorganisms.

Thus, this review aims to illustrate the current state of the art in biosensors and strip tests development for Vibrio monitoring. We directly noticed that the large majority of the devices designed for Vibrio detection was focused on the analysis of species pathogenic for human, especially V. cholerae. Surprisingly, despite the important economic losses attributed to some Vibrio in aquaculture, the use of biosensing platforms in this area is still in its infancy (Bonnin-Jusserand et al., 2017). We chose to deal with whole cell and nucleic acid detection since tools developed for human Vibrio can be transfered to the analysis of environmental Vibrio, notably those responsible for diseases in aquaculture settings. Toxin detection, restricted to V. cholerae, was not addressed (Cecchini et al., 2016). We showed that each of the described device has its own advantages and disadvantages.

Although strip tests constitute fast, low cost and easy-to-use devices, results are mostly qualitative or semi-quantitative (Sajid et al., 2015). Thus, strip tests are often used to perform a preliminary screening which can be confirmed by fully quantitative methods, such as biosensors. Compared to optical biosensors, the sensitivity and specificity of the electrochemical detection is restricted (Velusamy et al., 2010). However, due to their low cost and their miniaturization capacities, electrochemical devices are nowadays preferred by most end users.

The sensitivity of the developed tools is a critical point for bacteria detection. Thus, pushing sensitivity towards single cell limit of detection is essential to prevent infections and to ensure environmental safety. Besides, the specificity of the developed devices constitutes another important aspect. However, in most of the studies presented here, this parameter was evaluated only on a limited number of targeted and non-targeted strains. Furthermore, the applicability of the devices was rarely tested on naturally contaminated samples.

In the case of nucleic acid analysis, the extraction is a critical step. Although the development of a microfluidic system integrating DNA extraction was recently reported [START_REF] Park | An integrated rotary microfluidic system with DNA extraction, loop-mediated isothermal amplification, and lateral flow strip based detection for point-of-care pathogen diagnostics[END_REF], efforts have still to be made to automate and incorporate the extraction step into biosensing platforms.

Another point that we have to emphasize is that the majority of the reviewed tools requires a preliminary amplification of the target, increasing analysis time.

These last years, nanotechnologies have attracted a great interest for the development and improvement of biosensors. We showed that the most recent devices designed for Vibrio detection, included nanomaterials such as nanoparticles, nanotubes and nanowires. The large specific surface area and the high electrical conductivity of these materials allow to enhance the performances of biosensors with increased sensitivities and lowered detection limits (Holzinger et al., 2104).

In conclusion, two levels could be considered to detect Vibrio in the environment using biosensing platforms. In order to rapidly diagnose and prevent the contamination directly on the point of care, the strip tests could constitute interesting screening systems. Then, biosensors could ensure Vibrio monitoring by performing repeated measures. However, although some biosensors allow analysis on the field, these devices are still mainly used in laboratory. In order to bring biosensors from the lab to the field, the future trend is towards the development of integrated systems incorporating all the analytical steps from sample preparation to data collection. The sample was added with LPs and CPs in the sample chamber, and moved to the detection chamber using a magnet. Detection was performed with TMB as the substrate of HRP. Reproduced from Ref. [START_REF] Park | Sensitive immunoassay-based detection of Vibrio parahaemolyticus using capture and labeling particles in a stationary liquid phase lab-on-a-chip[END_REF], with permission from Elsevier. Fig. 4 : Schematic illustration of SERS-based aptasensor for V. parahaemolyticus detection using SiO2@Au core/shell NPs as the substrate. Reproduced from Ref. [START_REF] Duan | Vibrio parahaemolyticus detection aptasensor using surface-enhanced Raman scattering[END_REF], with permission from Elsevier. Fig. 5 : The schematic diagram for the preparation of multi-functionalized graphene oxide and the ECL immunosensor. Reproduced from Ref. [START_REF] Sha | A label-free multifunctionalized graphene oxide based electrochemiluminscence immunosensor for ultrasensitive and rapid detection of Vibrio parahaemolyticus in seawater and seafood[END_REF], with permission from Elsevier.

Figure and table captions :

  have been prominently applied for Vibrio detection. Optical biosensors include a large number of subclasses based on absorption, reflection, refraction, dispersion, infrared, chemiluminescence, and fluorescence. These devices provide advantages of compactness, flexibility, and resistance to electrical noise (Narsaiah et al., 2012 ; Ahmed et al., 2014 ; Yoo and Lee, 2016). Electrochemical biosensors can be classified into amperometric/voltammetric, potentiometric, impedimetric and conductimetric, based on their observed parameters such as current, potential, impedance and conductance, respectively. They are fast, easy to use, cheap, small-sized and easily miniaturized (Ivnitski et al., 2000 ; Palchetti and Mascini, 2008 ; Ahmed et al., 2014).

Fig. 1 :

 1 Fig. 1 : General principle of biosensor devices.

Fig. 2 :

 2 Fig. 2 : Lateral flow strip test principle. (A) The sample is loaded on the sample pad ; (B) The antibodies conjugated to gold nanoparticles bind to the analyte ; (C) The analyte recognition leads to a response on the test line and the proper migration of the sample through the membrane is validated by a response on the control line.

Fig. 3 :

 3 Fig.3: Schematic representation of the detection principle. (a) Labeling particle and capture particle. (b) Detection process using the SLP LOC. The sample was added with LPs and CPs in the sample chamber, and moved to the detection chamber using a magnet. Detection was performed with TMB as the substrate of HRP. Reproduced from Ref.[START_REF] Park | Sensitive immunoassay-based detection of Vibrio parahaemolyticus using capture and labeling particles in a stationary liquid phase lab-on-a-chip[END_REF], with permission from Elsevier.

Fig. 6 :

 6 Fig. 6 : (a) A digital image of the integrated rotary microdevice (b) Schematic illustration of the integrated rotary microdevice for the DNA extraction, the LAMP reaction, and the lateral flow strip detection. (c-i) Schematic design of the solid phase DNA extraction unit and the fluorescence images of the FAM-labelled DNA adsorbed glass microbeads,(c-ii) Schematic image of the LAMP amplification of target DNA (c-iii) Schematics of a lateral flow strip which consists of a buffer loading pad, a conjugate pad that contains streptavidin coated gold NPs, a detection zone where an anti-Digoxigenin, an anti-Texas red, a biotin are immobilized in the test line 1, the test line 2 and the control line, respectively, and an absorbent pad. Reproduced from Ref.[START_REF] Park | An integrated rotary microfluidic system with DNA extraction, loop-mediated isothermal amplification, and lateral flow strip based detection for point-of-care pathogen diagnostics[END_REF], with permission from Elsevier.

Fig. 7 :

 7 Fig. 7 : Schematic illustration of the chemiluminescent DNA-based assay for Vibrio spp. detection [51].

Fig. 8 :

 8 Fig.8: Schematic drawing of electrochemical DNA biosensor based on polylactide-stabilized gold nanoparticles modified electrode. Reproduced from Ref.[START_REF] Nordin | Sensitive detection of multiple pathogens using a single DNA probe[END_REF], with permission from Elsevier.

  Figure 1

Figure 6 Luminol

 6 Figure 6

Table 1 :

 1 Characteristics of the strip tests developed for whole Vibrio cell detection. -: not defined.

Table 2 :

 2 Characteristics of the optical biosensors designed for whole Vibrio cell detection. -: not defined.

Table 3 :

 3 Characteristics of the electrochemical biosensors developed for whole Vibrio cell detection. -: not defined.

Table 4 :

 4 Characteristics of the strip tests developed for the detection of nucleic acids extracted from Vibrio bacteria.

Table 5 :

 5 Characteristics of the optical biosensors designed for the detection of nucleic acids extracted from Vibrio bacteria. -: not defined.

Table 6 :

 6 Characteristics of the electrochemical biosensors developed for the detection of nucleic acids extracted from Vibrio bacteria. -: not defined.

Table 1

 1

	Target	Principle	Bioreceptor	Reference method	Sensitivity	Specificity	Evaluation of real samples	Reference
	V. cholerae O1/O139	LFA (Crystal VC ® RDT)	Antibody	Culture of frozen stool or stool on filter paper	94.2%-100%	84-100%	Frozen stools and rapid collected on filter paper culture (6h) of stools	[58]
	V. cholerae O1/O139	LFA (Crystal VC ® RDT)	Antibody	Culture on rectal swabs (multiplex PCR when RDT + / culture -)	93-96%	92-98%	Rectal swabs with 4h enrichment in APW	[36]
	V. cholerae O1/O139	LFA RDT) (Crystal VC ®	Antibody	PCR on rectal swabs	97%	71-76%	Fresh, bulk stools	[31]
	V. cholerae O1	LFA (Crystal VC ® RDT)	Antibody	Culture of rectal swabs and bulk stools	93-97%	77-97%	Rectal swabs with 4h fresh and bulk stools enrichment in APW and	[59]
	V. cholerae O1/O139	LFA (Crystal VC ® RDT)	Antibody	PCR on wet filters inoculated with stool samples and wet filter paper surnageants	86.1%	100%	Stool samples with 4-6h enrichment in APW	[37]
	V. cholerae O1/O139	LFA (Crystal VC ® RDT)	Antibody	Culture of water samples	89%	100%	Spiked water samples with 6-24h enrichment in APW	[60]
		LFA					Watery stool samples
	V. cholerae O1	(Crystal VC ®	Antibody	Culture of watery stools	65.6-75%	91.8-98.4%	with/without 6h enrichment	[35]
		RDT)					in APW
		LFA
	V. cholerae O1	(Crystal VC ®	Antibody	Culture of rectal swabs	93%	49%	Fresh, bulk stools	[61]
		RDT)
		LFA
	V. cholerae O1	(Crystal VC ®	Antibody	Culture of bulk stools	93-94%	67-76%	Fresh, bulk stools	[30]
		RDT)
	V. cholerae O1/O139	LFA RDT) (Crystal VC®	Antibody	Culture of bulk stools	92%	73%	Fresh, bulk stools	[32]

Table 2

 2

	Target	Detection technique Bioreceptor	LOD	Specificity	Evaluation of real samples (% recoveries)	Reference
	V. cholerae O1	SPR	Antibody	10 5 cells mL -1	No cross reaction	-	[63]
	V. cholerae O1	SPR	Antibody	43 cells mL -1	No cross reaction	-	[64]
	V. alginolyticus	Fluorescence	Antibody	2.8 x 10 2 CFU mL -1 No cross reaction	Spiked shrimp samples (89.4-94.0%) Fishpond water (95.9-102.3%)	[28]
	V. parahaemolyticus	Colorimetry	Antibody	100 cells mL -1	No cross reaction	Spiked oyster samples (-)	[27]
	V. parahaemolyticus	Fluorescence	Aptamer	35 CFU mL -1	No cross reaction	Spiked shrimp samples (-)	[29]
	V. parahaemolyticus	Colorimetry	Aptamer	10 CFU mL -1	No cross reaction	Spiked water (92.0-102.0%)	[24]
						Spiked shrimp samples (91.0-97.8%)
	V. parahaemolyticus	SERS	Aptamer	10 CFU mL -1	No cross reaction	Seawater (99.4-101.0%)	[25]
						Groundwater (98.0-100.6%)
	SERS : Surface Enhanced Raman Spectroscopy ; SPR : Surface Plasmon Resonance

Table 4

 4

	Target (gene)	Principle	Bioreceptor	LOD	Specificity	Evaluation of real samples (LOD)	Reference
	V. cholerae (lolB)	PCR + LFA	Antibody	5 ng of amplicons	No cross reaction	Spiked stool samples	[70]
	V. cholerae (ctxA)	LATE-PCR + LFA	DNA probe	1 pg of genomic DNA 10 CFU mL -1	No cross reaction	Spiked stool samples	[45]
	V. alginolyticus (rpoX)	LAMP + LFA	DNA probe	1.8 x 10 2 CFU mL -1	No cross reaction	Spiked whiteleg shrimp (2.0 x 10 3 CFU g -1 ) samples	[43]
	V. parahaemolyticus (tlh)	LAMP + LFA	DNA probe	120 CFU mL -1	No cross reaction	Spiked shrimp samples (1.8 x 10 3 CFU g -1 )	[48]
	V. harveyi (vvhP2)	LAMP + LFA	DNA probe	1.1 x 10 2 CFU mL -1	No cross reaction	Spiked shrimp samples (1.8 x 10 3 CFU g -1 )	[49]
	V. vulnificus (rpoS)	LAMP + LFA	DNA probe	1.5 x 10 3 CFU mL -1	No cross reaction	Spiked oyster samples (1.2 x 10 4 CFU g -1 )	[42]
	V. parahaemolyticus (tlh)	CPA + vertical flow	Antibody	1.8 CFU mL -1	No cross reaction	Spiked oyster samples (18 CFU g -1 )	[41]
	V. parahaemolyticus (toxR)	MCDA + LFA	Antibody	10 fg of DNA 4.2 x 10 2 CFU mL -1	No cross reaction	Spiked oyster homogenates (4.2 x 10 2 CFU g -1 )	[71]
	V. parahaemolyticus (toxR)	Microfluidic system incorporating LAMP + LFA	Antibody	10 4 CFU mL -1	No cross reaction	Spiked milk samples (5.0 x 10 3 CFU/5µL)	[52]

LFA : Lateral Flow Assay ; LATE-PCR : Linear After The Exponential PCR ; LAMP : Loop mediated isothermal AMplification ; CPA : Cross Priming Amplification ; MCDA : Multiple Cross Displacement Amplification

Table 5

 5

	Target (gene)	PCR amplification	Detection technique	Bioreceptor	LOD	Specificity	Evaluation of real samples (LOD)	Reference
	V. vulnificus,
	V. cholerae, V. parahaemolyticus	Yes	Colorimetry	DNA probe	-	No cross reaction	Oyster tissue homogenates (10 2 CFU g -1 )	[72]
	(vvh, ctx, tlh)
	V. cholerae (nd)	No	Photoluminescence	DNA probe	3.133 ng µL -1	-	-	[50]
	V. cholerae (ompW)	No	Fluorescence	DNA probe	2.34 ng mL -1	No cross reaction	-	[56]
	Vibrio spp. (16S rRNA)	No	Chemiluminesc-ence	DNA probe	5 ng µL -1	No cross reaction	Phytoplankton and spiked seawater (nd)	[51]

Table 6

 6 DPASV : Differential Pulse Anodic Stripping Voltammetry ; DPV : Differential Pulse Voltammetry ; EIS : Electrochemical Impedance Spectroscopy

	Target (gene)	PCR amplification	Detection technique	Bioreceptor	LOD	Specificity	Evaluation of real samples (LOD)	Reference
	V. cholerae (lolB)	Yes	Intermitent Pulse Amperometry	DNA probe	10 CFU mL -1	No cross reaction	-	[38]
	V. cholerae (lolB)	Yes	Chrono amperometry	DNA probe	0.85 ng µL -1	No cross reaction	-	[39]
	V. cholerae (toxR)	Yes	Amperometry	DNA probe	8-61 pM	No cross reaction	Spiked stools (-)	[53]
	V. cholerae (toxR)	Yes	Amperometry	DNA probe	10 CFU mL -1	No cross reaction	Spiked stools (-)	[40]
	V. cholerae (lolB)	Yes	DPASV	DNA probe	5 pg µL -1	No cross reaction	Spiked stools (10 3 CFU mL -1 )	[74]
	V. cholerae (lolB)	Yes	DPASV	DNA probe	-	No cross reaction	Spiked stools (2 CFU mL -1 )	[46]
	V. cholerae (lolB)	Yes	DPASV	DNA probe	0.5 ng mL -1 10 CFU mL -1	No cross reaction	Spiked stools (-)	[47]
	V. cholerae (lolB)	Yes	DPASV	DNA probe	1 fM	No cross reaction	-	[44]
	V. cholerae O1 (nd)	No	DPV	DNA probe	35.2 ng µL -1	-	-	[54]
	V. cholerae O1 (nd)	No	EIS	DNA probe	21.7 ng µL -1	-	Human blood/serum (-)	[55]
	V. parahaemolyticus (nd)	No	DPV	DNA probe	2.6 pM	No cross reaction	Spiked cockle samples (-)	[57]

Acknowledgements

Authors would like to acknowledge the University of Perpignan Via Domitia, France, for its financial support through Doctoral School 305.

V. parahaemolyticus Electrochemiluminescence Antibody 5 CFU mL -1 No cross reaction Spiked seawater (5 CFU mL -1 ) and seafood (5 CFU g -1 ) [START_REF] Sha | A label-free multifunctionalized graphene oxide based electrochemiluminscence immunosensor for ultrasensitive and rapid detection of Vibrio parahaemolyticus in seawater and seafood[END_REF]