Environmental investigations of Vibrio parahaemolyticus in oysters after outbreaks in Washington, Texas, and New York (1997 and 1998)

Serodiversity, antibiotic resistance, and virulence genes of Vibrio parahaemolyticus in oysters collected in coastal areas of northwestern Mexico between 2012 and 2020

This study aimed to determine the prevalence of V. parahaemolyticus in oysters from the northwestern coast of Mexico and to identify the serotypes, virulence factors, and antibiotic resistance of the strains. Oyster samples were collected from 2012 to 2020 from the northwest coast of Mexico; biochemical and molecular methods were used to identify V. parahaemolyticus from oysters; antiserum reaction to determine V. parahaemolyticus serotypes, and PCR assays were performed to identify pathogenic (tdh and/or trh) or pandemic (toxRS/new, and/or orf8) strains and antibiotic resistance testing. A total of 441 oyster samples were collected and tested for V. parahaemolyticus. Forty-seven percent of oyster samples were positive for V. parahaemolyticus. Ten different O serogroups and 72 serovars were identified, predominantly serotype O1:KUT with 22.2% and OUT:KUT with 17.3%. Twenty new serotypes that had not been previously reported in our region were identified. We detected 4.3% of pathogenic clones but no pandemic strains. About 73.5% of strains were resistant to at least one antibiotic, mainly ampicillin and ciprofloxacin; 25% were multi-drug resistant. In conclusion, the pathogenic strains in oysters and antibiotic resistance are of public health concern, as the potential for outbreaks throughout northwestern Mexico is well established.

Genomic diversity of Vibrio spp. and metagenomic analysis of pathogens in Florida Gulf coastal waters following Hurricane Ian

IMPORTANCE

Evidence suggests warming temperatures are associated with the spread of potentially pathogenic Vibrio spp. and the emergence of human disease globally. Following Hurricane Ian, the State of Florida reported a sharp increase in the number of reported Vibrio spp. infections and deaths. Hence, monitoring of pathogens, including vibrios, and environmental parameters influencing their occurrence is critical to public health. Here, DNA sequencing was used to investigate the genomic diversity of Vibrio parahaemolyticus and Vibrio vulnificus, both potential human pathogens, in Florida coastal waters post Hurricane Ian, in October 2022. Additionally, the microbial community of water samples was profiled to detect the presence of Vibrio spp. and other microorganisms (bacteria, fungi, protists, and viruses) present in the samples. Long-term environmental data analysis showed changes in environmental parameters during and after Ian were optimal for the growth of Vibrio spp. and related pathogens. Collectively, results will be used to develop predictive risk models during climate change.

Tools to Enumerate and Predict Distribution Patterns of Environmental Vibrio vulnificus and Vibrio parahaemolyticus

Vibrio vulnificus (Vv) and Vibrio parahaemolyticus (Vp) are water- and foodborne bacteria that can cause several distinct human diseases, collectively called vibriosis. The success of oyster aquaculture is negatively impacted by high Vibrio abundances. Myriad environmental factors affect the distribution of pathogenic Vibrio, including temperature, salinity, eutrophication, extreme weather events, and plankton loads, including harmful algal blooms. In this paper, we synthesize the current understanding of ecological drivers of Vv and Vp and provide a summary of various tools used to enumerate Vv and Vp in a variety of environments and environmental samples. We also highlight the limitations and benefits of each of the measurement tools and propose example alternative tools for more specific enumeration of pathogenic Vv and Vp. Improvement of molecular methods can tighten better predictive models that are potentially important for mitigation in more controlled environments such as aquaculture.

Evaluation of Alternative Colony Hybridization Methods for Pathogenic Vibrios

Vibrios, such as Vibrio parahaemolyticus, are naturally occurring halophilic bacteria that are a major cause of foodborne illness. Because of their autochthonous nature, managing vibrio levels in marine and estuarine environments is impossible. Instead, it is crucial to reliably enumerate their abundance to minimize human exposure. One method of achieving this is the direct plating/colony hybridization (DP/CH) method, which has been used to efficiently quantify pathogenic vibrios in oysters and other seafood products. Although successful, the method relies on proprietary resources. We examined alternative approaches, assessed the influence of the reagent suppliers’ source on enumeration accuracy, and made experimental adjustments that maximized efficiency, sensitivity, and specificity. We report here that in-house conjugation via Cell Mosaic is a viable alternative to the previously available sole-source distributor of the alkaline phosphatase-conjugated probes used to enumerate vibrios in oysters. We also report that milk was a viable alternative as a blocking reagent, pH must be eight, an orbital shaker was a viable alternative to a water bath, and narrow polypropylene containers were a viable alternative to Whirl-Pak bags. These modifications will be crucial to scientists enumerating vibrios and other pathogens in food products.

Environmental Reservoirs of Pathogenic Vibrio spp. and Their Role in Disease: The List Keeps Expanding

Vibrio species are natural inhabitants of aquatic environments and have complex interactions with the environment that drive the evolution of traits contributing to their survival. These traits may also contribute to their ability to invade or colonize animal and human hosts. In this review, we attempt to summarize the relationships of Vibrio spp. with other organisms in the aquatic environment and discuss how these interactions could potentially impact colonization of animal and human hosts.

Comparative analysis unravels genetic recombination events of Vibrio parahaemolyticus recA gene

Vibrio parahaemolyticus is a gram-negative bacterium capable of causing diseases in humans and aquatic animals. The global relationships among V. parahaemolyticus genomes have been studied using multilocus sequence typing (MLST). Recently, the MLST gene recA has shown difficulties in amplification and/or a larger PCR fragment for some V. parahaemolyticus genomes due to genetic recombination. We aimed to investigate these recombination events of recA gene by analyzing 500 publicly available whole genomes from the NCBI database. The genomes with untypable recA genes were separated using BIGSdb and CGEMLST 2.0 servers, followed by annotation with RAST and NCBI pipelines. Moreover, the variable nature of V. parahaemolyticus was investigated by wgMLST analysis. The hypothetical proteins in recombinant regions were analyzed with VCIMPred tool. In the results, 3 genomes were detected with recA gene recombination, in which 2 were associated with phages and 1 to an AHPND causing strain. All 3 recombinant regions had a G + C content of 39%-40% with 15-30 ORFs, including a newly incorporated recA gene. These acquired recA genes were closely related to 3 different genera namely Aliivibrio, Photobacterium, and Vibrio. The wgMLST analysis indicated genetic recombination events occur independently among V. parahaemolyticus on a global scale. The in silico analysis revealed 4 hypothetical proteins associated with virulence factors in recombinant regions. The present study confirms, recombination events of V. parahaemolyticus recA gene, are diverse and may have an impact on the evolutionary process. Moreover, understanding these genetic recombination events of the recA gene is necessary to determine their STs and, therefore assessing epidemiological relationships.

A systematic review and meta-analysis on antimicrobial resistance in marine bivalves

Bivalves are filter-feeding animals able to accumulate contaminants and microorganisms, either of marine or terrestrial origin. The aim of this study was to describe the prevalence of antimicrobial resistance (AMR) in bacterial isolates from bivalves using a systematic review of the literature. Comprehensive searches of MEDLINE, EMBASE, and Web of Science were carried out, based upon a registered protocol (PROSPERO), and following the preferred Reporting Items for Systematic reviews and Meta-Analysis (PRISMA) guidelines. The methodological quality of the included studies was assessed using a modified Hoy checklist. Meta-analyses of prevalence were carried out using random-effects models. In total, 103 articles were selected from 1,280 records and were included in the final analysis. The studies were from Asia (n = 54), Europe (n = 27), South and North America (n = 10 and n = 6, respectively), Africa (n = 2), Oceania (n = 1), and multicentre and intercontinental (n = 3). The meta-analysis of multiple antibiotic resistance (MAR) index revealed Aeromonas spp. as the genus with the highest prevalence of AMR (37%), followed by Vibrio spp. (34%), Salmonella spp. (18%), and Escherichia coli (15%). Resistance to third/fourth/fifth generation cephalosporins and fluoroquinolones, two highest priority, critically important antimicrobials (HPCIA), was recorded in approximately 10% of E. coli isolates. Resistance to carbapenems was very low (<2%) in Salmonella spp. and in E. coli, but was found in 5% of Vibrio spp. and in more than a third of Aeromonas spp. isolates. In aquatic bacteria, resistance to carbapenems was higher in Asian than in European isolates. Our study shows the presence of antibiotic resistant bacteria (ARB), including bacteria resistant to HPCIA, in marine bivalves, posing a risk for consumers.

Vibrio parahaemolyticus Is Associated with Diarrhea Cases in Mexico, with a Dominance of Pandemic O3:K6 Clones

In the present study, we conducted surveillance of the V. parahaemolyticus strains present in clinical samples from six geographical regions of Mexico (22 states) from 2004 to 2011. The serotype dominance, virulence genes, presence of pandemic O3:K6 strains, and antibiotic resistance of the isolates were investigated. In total, 144 strains were isolated from the clinical samples. Seven different O serogroups and twenty-five serovars were identified. Most clinical isolates (66%, 95/144) belonged to the pandemic clone O3:K6 (tdh+, toxRS/new+ and/or orf8+) and were detected in 20 of the 22 states. Among the pandemic clones, approximately 17.8% (17/95) of the strains cross-reacted with the antisera for the K6 and K59 antigens (O3:K6, K59 serotype). Other pathogenic strains (tdh+ and/or trh+, toxRS/new-, orf8-) accounted for 26.3%, and the nonpathogenic strains (tdh- and/or trh-) accounted for 7.6%. Antimicrobial susceptibility testing showed that most of the strains were resistant to ampicillin (99.3%) but were sensitive to most tested antibiotics. The level of multidrug resistance was 1.3%. Our results indicate that pandemic O3:K6 is present in most Mexican states, thus, constant surveillance of V. parahaemolyticus strains in diarrhea patients is a public health priority and is useful for conducting risk assessments of foodborne illnesses to prevent V. parahaemolyticus outbreaks. Overall, our observations indicate that the pandemic O3:K6 clone of V. parahaemolyticus has become a relatively stable subpopulation and may be endemically established in Mexico; therefore, constant surveillance is needed to avoid new outbreaks of this pathogen.

Genomic Characterization of Ciprofloxacin Resistance in Laboratory-Derived Mutants of Vibrio parahaemolyticus

The quinolone ciprofloxacin is a broad-spectrum bactericidal antibiotic used for human medicine as well as the aquaculture industry. The emergence of ciprofloxacin-resistant Vibrio parahaemolyticus strains is currently a global public health concern. However, the mechanism of ciprofloxacin resistance in V. parahaemolyticus is not yet fully clarified. We generated mutants with decreased ciprofloxacin susceptibility using in vitro selection and investigated genes associated with ciprofloxacin resistance on a genetic level. Our selection process yielded mutants that possessed altered minimal inhibitory concentrations (MICs) for ciprofloxacin and other unrelated antibiotics. These included Ser83Ile mutations in GyrA and Val461Glu in ParE as well as mutations in the resistance nodulation cell division (RND) family transporter gene vmeD and the putative TetR family regulator gene vp0040 upstream of the vmeCD operon. Measurements of steady-state mRNA levels revealed that the ciprofloxacin-resistant mutants overexpressed vmeCD. Further, the introduction of the vp0040 mutated allele from H512 into the sensitive parental strain increased the MIC for ciprofloxacin 31.25-fold. Taken together, these results indicated that ciprofloxacin resistance in these mutants was due to the quinolone resistance determining region mutation as well as overexpression of vmeCD caused by a loss of vp0040 gene repression. This also accounted for the presence of the multidrug resistance phenotype for these mutant strains since RND efflux system can export structurally unrelated antibiotics.

Depuration of live oysters to reduce Vibrio parahaemolyticus and Vibrio vulnificus: A review of ecology and processing parameters

Consumption of raw oysters, whether wild-caught or aquacultured, may increase health risks for humans. Vibrio vulnificus and Vibrio parahaemolyticus are two potentially pathogenic bacteria that can be concentrated in oysters during filter feeding. As Vibrio abundance increases in coastal waters worldwide, ingesting raw oysters contaminated with V. vulnificus and V. parahaemolyticus can possibly result in human illness and death in susceptible individuals. Depuration is a postharvest processing method that maintains oyster viability while they filter clean salt water that either continuously flows through a holding tank or is recirculated and replenished periodically. This process can reduce endogenous bacteria, including coliforms, thus providing a safer, live oyster product for human consumption; however, depuration of Vibrios has presented challenges. When considering the difficulty of removing endogenous Vibrios in oysters, a more standardized framework of effective depuration parameters is needed. Understanding Vibrio ecology and its relation to certain depuration parameters could help optimize the process for the reduction of Vibrio. In the past, researchers have manipulated key depuration parameters like depuration processing time, water salinity, water temperature, and water flow rate and explored the use of processing additives to enhance disinfection in oysters. In summation, depuration processing from 4 to 6 days, low temperature, high salinity, and flowing water effectively reduced V. vulnificus and V. parahaemolyticus in live oysters. This review aims to emphasize trends among the results of these past works and provide suggestions for future oyster depuration studies.

Nested Spatial and Temporal Modeling of Environmental Conditions Associated With Genetic Markers of Vibrio parahaemolyticus in Washington State Pacific Oysters

The Pacific Northwest (PNW) is one of the largest commercial harvesting areas for Pacific oysters (Crassostrea gigas) in the United States. Vibrio parahaemolyticus, a bacterium naturally present in estuarine waters accumulates in shellfish and is a major cause of seafood-borne illness. Growers, consumers, and public-health officials have raised concerns about rising vibriosis cases in the region. Vibrio parahaemolyticus genetic markers (tlh, tdh, and trh) were estimated using an most-probable-number (MPN)-PCR technique in Washington State Pacific oysters regularly sampled between May and October from 2005 to 2019 (N = 2,836); environmental conditions were also measured at each sampling event. Multilevel mixed-effects regression models were used to assess relationships between environmental measures and genetic markers as well as genetic marker ratios (trh:tlh, tdh:tlh, and tdh:trh), accounting for variation across space and time. Spatial and temporal dependence were also accounted for in the model structure. Model fit improved when including environmental measures from previous weeks (1-week lag for air temperature, 3-week lag for salinity). Positive associations were found between tlh and surface water temp, specifically between 15 and 26°C, and between trh and surface water temperature up to 26°C. tlh and trh were negatively associated with 3-week lagged salinity in the most saline waters (> 27 ppt). There was also a positive relationship between tissue temperature and tdh, but only above 20°C. The tdh:tlh ratio displayed analogous inverted non-linear relationships as tlh. The non-linear associations found between the genetic targets and environmental measures demonstrate the complex habitat suitability of V. parahaemolyticus. Additional associations with both spatial and temporal variables also suggest there are influential unmeasured environmental conditions that could further explain bacterium variability. Overall, these findings confirm previous ecological risk factors for vibriosis in Washington State, while also identifying new associations between lagged temporal effects and pathogenic markers of V. parahaemolyticus.

Characterization of Pathogenic Vibrio parahaemolyticus Isolated From Fish Aquaculture of the Southwest Coastal Area of Bangladesh

Vibrio parahaemolyticus is a major foodborne pathogen responsible for significant economic losses in aquaculture and a threat to human health. Here, we explored the incidence, virulence potential, and diversity of V. parahaemolyticus isolates from aquaculture farms in Bangladesh. We examined a total of 216 water, sediment, Oreochromis niloticus (tilapia), Labeo rohita (rui), and Penaeus monodon (shrimp) samples from the aquaculture system where 60.2% (130/216) samples were positive for V. parahaemolyticus. Furthermore, we identified 323 V. parahaemolyticus strains from contaminated samples, 17 of which were found positive for trh, a virulence gene. Four isolates out of the 17 obtained were able to accumulate fluid in the rabbit ileal loop assay. The correlation between the contamination of V. parahaemolyticus and environmental factors was determined by Pearson correlation. The temperature and salinity were significantly correlated (positive) with the incidence of V. parahaemolyticus. Most of the pathogenic isolates (94.1%) were found resistant to ampicillin and amoxicillin. O8: KUT was the predominant serotype of the potentially pathogenic isolates. ERIC-PCR reveals genetic variation and relatedness among the pathogenic isolates. Therefore, this region-specific study establishes the incidence of potential infection with V. parahaemolyticus from the consumption of tilapia, rui, and shrimp raised in farms in Satkhira, Bangladesh, and the basis for developing strategies to reduce the risk for diseases and economic burden.

Identification of Genes Associated with Sensitivity to Ultraviolet A (UVA) Irradiation by Transposon Mutagenesis of Vibrio parahaemolyticus

Ultraviolet (UV) irradiation is used to disinfect water and food and can be classified as UVA (detected at wavelengths 320–400 nm), UVB (280–320 nm), and UVC (<280 nm). We developed a method for UVA sterilization of equipment with a UVA-light-emitting diode (LED); however, a high rate of fluence was needed to promote pathogen inactivation. The aim of this study was to identify genes associated with UVA sensitivity with the goal of improving UVA-LED-mediated bactericidal activity. We constructed a transposon-mutant library of Vibrio parahaemolyticus and selected six mutants with high sensitivity to UVA irradiation. Genes associated with this phenotype include F-type H+-transporting ATPases (atp), as well as those involved in general secretion (gsp), and ubiquinone and terpenoid-quinone biosynthesis (ubi). Gene complementation resulted in decreased sensitivity to UVA-LED. The atp mutants had lower intracellular adenosine triphosphate (ATP) concentrations than the wild-type treatment, with 20 mM L-serine resulting in elevated ATP concentrations and decreased sensitivity to UVA-LED. The gsp mutants exhibited high levels of extracellular protein transport and the ubi mutants exhibited significantly different intracellular concentrations of ubiquinone-8. Taken together, our results suggest that the protein products of the atp, gsp, and ubi genes may regulate sensitivity to UVA irradiation.

Potentially human pathogenic Vibrio spp. in a coastal transect: Occurrence and multiple virulence factors

An increase in human Vibrio spp. infections has been linked to climate change related events, in particular to seawater warming and heatwaves. However, there is a distinct lack of research of pathogenic Vibrio spp. occurrences in the temperate North Sea, one of the fastest warming seas globally. Particularly in the German Bight, Vibrio investigations are still scarce. This study focuses on the spatio-temporal quantification and pathogenic characterization of V. parahaemolyticus, V. vulnificus and V. cholerae over the course of 14 months. Species-specific MPN-PCR (Most probable number - polymerase chain reaction) conducted on selectively enriched surface water samples revealed seasonal patterns of all three species with increased abundances during summer months. The extended period of warm seawater coincided with prolonged Vibrio spp. occurrences in the German Bight. Temperature and nitrite were the factors explaining variations in Vibrio spp. abundances after generalized additive mixed models. The specific detection of pathogenic markers via PCR revealed trh-positive V. parahaemolyticus, pathogenic V. vulnificus (nanA, manIIA, PRXII) and V. cholerae serotype O139 presence. Additionally, spatio-temporally varying virulence profiles of V. cholerae with multiple accessory virulence-associated genes, such as the El Tor variant hemolysin (hlyAET), acyltransferase of the repeats-in-toxin cluster (rtxC), Vibrio 7th pandemic island II (VSP-II), Type III Secretion System (TTSS) and the Cholix Toxin (chxA) were detected. Overall, this study highlights that environmental human pathogenic Vibrio spp. comprise a reservoir of virulence-associated genes in the German Bight, especially in estuarine regions. Due to their known vast genetic plasticity, we point to the possible emergence of highly pathogenic V. cholerae strains. Particularly, the presence of V. cholerae serotype O139 is unusual and needs urgent continuous surveillance. Given the predictions of further warming and more frequent heatwave events, human pathogenic Vibrio spp. should be seriously considered as a developing risk to human health in the German Bight.

Attenuation of Vibrio parahaemolyticus Virulence Factors by a Mixture of Natural Antimicrobials

Reducing acute mortality in aquatic crustaceans using natural alternatives to antibiotics has become a necessity, firstly for its positive impact on the aquaculture industry and, secondly, because the extensive use of antibiotics may lead to increased levels of drug resistance in pathogenic microorganisms. This study aimed to investigate the effect of a mixture of natural antimicrobials on the in vitro and in vivo virulence abilities of Type VI secretion system (T6SS)-positive Vibrio parahaemolyticus (A3 and D4), strains known as having potentially harmful health consequences for aquatic crustaceans and consumers. Herein, we report that a natural antimicrobial mixture (A3009) was capable of significantly reducing the virulence of V. parahaemolyticus strains A3 and D4 in an in vitro infection model, using the fish cell line CHSE-214, an effect which correlates with the bacterial downregulation of hcp1 and hcp2 gene expression and with the ability of the antimicrobial to efficiently retain low cytotoxic levels (p < 0.001). We show for the first time that a natural antimicrobial is able to significantly reduce the mortality of shrimps in a challenge experiment and is able to significantly attenuate H₂O₂ release during infection (p < 0.001), indicating that it could harbor positive intestinal redox balance effects.

Bacteriophages Against Pathogenic Vibrios in Delaware Bay Oysters (Crassostrea virginica) During a Period of High Levels of Pathogenic Vibrio parahaemolyticus

Eastern oysters (Crassostrea virginica) from three locations along the Delaware Bay were surveyed monthly from May to October 2017 for levels of total Vibrio parahaemolyticus, pathogenic strains of V. parahaemolyticus and Vibrio vulnificus, and for strain-specific bacteriophages against vibrios (vibriophages). The objectives were to determine (a) whether vibriophages against known strains or serotypes of clinical and environmental vibrios were detectable in oysters from the Delaware Bay and (b) whether vibriophage presence or absence corresponded with Vibrio abundances in oysters. Host cells for phage assays included pathogenic V. parahaemolyticus serotypes O3:K6, O1:KUT (untypable) and O1:K1, as well as clinical and environmental strains of V. vulnificus. Vibriophages against some, but not all, pathogenic V. parahaemolyticus serotypes were readily detected in Delaware Bay oysters. In July, abundances of total and pathogenic V. parahaemolyticus at one site spiked to levels exceeding regulatory guidelines. Phages against three V. parahaemolyticus host serotypes were detected in these same oysters, but also in oysters with low V. parahaemolyticus levels. Serotype-specific vibriophage presence or absence did not correspond with abundances of total or pathogenic V. parahaemolyticus. Vibriophages were not detected against three V. vulnificus host strains, even though V. vulnificus were readily detectable in oyster tissues. Selected phage isolates against V. parahaemolyticus showed high host specificity. Transmission electron micrographs revealed that most isolates were ~ 60-nm diameter, non-tailed phages. In conclusion, vibriophages were detected against pandemic V. parahaemolyticus O3:K6 and O1:KUT, suggesting that phage monitoring in specific host cells may be a useful technique to assess public health risks from oyster consumption.

Piper betel Compounds Piperidine, Eugenyl Acetate, and Chlorogenic Acid Are Broad-Spectrum Anti-Vibrio Compounds that Are Also Effective on MDR Strains of the Pathogen

The natural population of the aquatic environment supports a diverse aquatic biota and a robust seafood industry. However, this environment also provides an appropriate niche for the growth of pathogenic bacteria that cause problems for human health. For example, species of the genus Vibrio inhabit marine and estuarine environments. This genus includes species that are pathogenic to aquaculture, invertebrates, and humans. In humans, they can cause prominent diseases like gastroenteritis, wound infections, and septicemia. The increased number of multidrug resistant (MDR) Vibrio strains has drawn the attention of the scientific community to develop new broad-spectrum antibiotics. Hence, in this paper we report the bactericidal effects of compounds derived from Piper betel plants: piperidine, chlorogenic acid, and eugenyl acetate, against various strains of Vibrio species. The different MIC90 values were approximately in a range of 2–6 mg/mL, 5–16 mg/mL, 5–20 mg/mL, and 30–80 mg/mL, for piperidine, chlorogenic acid, and eugenyl acetate, respectively. Piperidine showed the best anti-Vibrio effect against the five Vibrio species tested. Interestingly, combinations of sub-inhibitory concentrations of piperidine, chlorogenic acid, and eugenyl acetate showed inhibitory effects in the Vibrio strains. Furthermore, these compounds showed synergism or partial synergism effects against MDR strains of the Vibrio species when they were incubated with antibiotics (ampicillin and chloramphenicol).

Loop-mediated isothermal amplification assay as a point-of-care diagnostic tool for Vibrio parahaemolyticus: recent developments and improvements

INTRODUCTION

A number of DNA-based diagnostic tools have been developed for the detection of Vibrio parahaemolyticus in seafood. However, the loop-mediated isothermal amplification (LAMP) has distinct advantages with regards to its simplicity, speed and the ease of performing without any need for sophisticated equipment. Over the last decade, LAMP has emerged as a potential tool for the detection of V. parahaemolyticus. Area covered: The literature search was restricted to LAMP assay and its variants for the detection of V. parahaemolyticus. The focus in this review is to enlist the various techniques that have been developed using the principle of the LAMP towards improved simplicity, sensitivity and specificity of the assay. Expert commentary: LAMP assay and its variants are significantly faster and require minimum accessories compared to other DNA based molecular techniques such as PCR and their types. Despite the availability of several versions, LAMP-based diagnostics is not the first choice for the detection of V. parahaemolyticus in the seafood sector. Our recommendation would be to explore the possibilities of developing cost-effective LAMP kits and implementing these kits as point-of-care diagnostic tools for rapid and sensitive detection of pathogenic V. parahaemolyticus.

Comparative performance of TCBS and TSA for the enumeration of trh+ Vibrio parahaemolyticus by direct colony hybridization

Vibrio parahaemolyticus is one of the important foodborne pathogens is of public health concern due to the emergence of pandemic strains causing disease outbreaks worldwide. We evaluated the DNA based colony hybridization technique for the detection and enumeration of total and pathogenic V. parahaemolyticus from the bivalve shellfish, clam using non-radioactive, enzyme-labeled probe targeting the tlh and trh genes, respectively. The digoxigenin (DIG) labeled probes designed in this study showed 100% specificity by dot blot assay. Colony hybridization using DIG probes was performed using both non-selective, trypticase soy agar (TSA) and the selective medium, thiosulfate citrate bile salts sucrose (TCBS) agar. Of 32 clam samples analyzed, 71.88% had>10,000 V. parahaemolyticus cells/g in TSA whereas it was 18.75% in case of TCBS. All the samples showed the presence of total V. parahaemolyticus in TSA and 97% in the case of TCBS. Interestingly, results of the trh⁺V. parahaemolyticus samples were quite high while using TCBS plates (62.5%) as compared to TSA (43.75%). However, the cell numbers obtained from TSA were higher than from TCBS. Several yellow colonies on TCBS turned out to be V. parahaemolyticus using colony hybridization, which was further confirmed by PCR and sucrose utilization test. Colony hybridization using DIG-labeled probe was found to be highly sensitive and could differentiate and enumerate pathogenic and non-pathogenic strains of V. parahaemolyticus. Since traditional methods are not only labor-intensive and time-consuming but also less sensitive, colony hybridization using DIG-labeled probes would be a useful alternative for the enumeration of V. parahaemolyticus in naturally contaminated seafood.

Combination of Multilocus Sequence Typing and GS-PCR Reveals an Association of Pandemic Vibrio parahaemolyticus Clone with Clinical and Seafood Isolates

Vibrio parahaemolyticus is a global leading cause of seafood-borne bacterial gastroenteritis. Clinical, seafood, and environmental V. parahaemolyticus isolates from the eastern coast of China were analyzed for their virulence, and for phenotypic and molecular traits. The frequency of pandemic isolates was 50.9% among clinical isolates and 42.8% among seafood isolates as confirmed by group-specific polymerase chain reaction (GS-PCR). Serological analysis indicated that O3:K6, O1:K25, O1:KUT, O3:K68, and O4:K68 were the predominant serotypes among these pandemic isolates. It is worth noting that the pandemic serotypes were not exclusively identified from clinical samples. Rather, they were also isolated from seafood samples. It was also shown by multilocus sequence typing (MLST) typing that isolates from clinical (59), seafood (28), and environmental samples (18) were grouped into 17, 23, and 17 sequence types (STs), respectively. We updated 17 STs in the MLST database. ST-3 and ST-189 were the dominant ones among clinical isolates. Interestingly, ST-3 was also the most abundant among seafood isolates, and represented a significant risk to food safety due to the clear association with tdh and the GS-PCR marker. A minimum-evolution (ME) tree generated from the concatenated sequences of the 7 loci of the 54 STs uncovered phylogenetic relationships between seafood and clinical isolates. The MLST results also indicated a high degree of nucleotide diversity in recA that had the greatest influence on the phylogenetic relationships. Our findings provided new insight into the phylogenic relationship among pandemic V. parahaemolyticus isolates from various samples and enhanced the MLST database as well as microbiological risk assessment.

PRACTICAL APPLICATION

Pandemic V. parahaemolyticus isolates have become a serious public health concern. This study demonstrated the characteristics of clinical and seafood V. parahaemolyticus isolates, and determined the phylogenetic relatedness among them. These results can be used for microbiological risk assessment in China.

Potential Survival and Pathogenesis of a Novel Strain, Vibrio parahaemolyticus FORC_022, Isolated From a Soy Sauce Marinated Crab by Genome and Transcriptome Analyses

Vibrio parahaemolyticus can cause gastrointestinal illness through consumption of seafood. Despite frequent food-borne outbreaks of V. parahaemolyticus, only 19 strains have subjected to complete whole-genome analysis. In this study, a novel strain of V. parahaemolyticus, designated FORC_022 (Food-borne pathogen Omics Research Center_022), was isolated from soy sauce marinated crabs, and its genome and transcriptome were analyzed to elucidate the pathogenic mechanisms. FORC_022 did not include major virulence factors of thermostable direct hemolysin (tdh) and TDH-related hemolysin (trh). However, FORC_022 showed high cytotoxicity and had several V. parahaemolyticus islands (VPaIs) and other virulence factors, such as various secretion systems (types I, II, III, IV, and VI), in comparative genome analysis with CDC_K4557 (the most similar strain) and RIMD2210633 (genome island marker strain). FORC_022 harbored additional virulence genes, including accessory cholera enterotoxin, zona occludens toxin, and tight adhesion (tad) locus, compared with CDC_K4557. In addition, O3 serotype specific gene and the marker gene of pandemic O3:K6 serotype (toxRS) were detected in FORC_022. The expressions levels of genes involved in adherence and carbohydrate transporter were high, whereas those of genes involved in motility, arginine biosynthesis, and proline metabolism were low after exposure to crabs. Moreover, the virulence factors of the type III secretion system, tad locus, and thermolabile hemolysin were overexpressed. Therefore, the risk of foodborne-illness may be high following consumption of FORC_022 contaminated crab. These results provided molecular information regarding the survival and pathogenesis of V. parahaemolyticus FORC_022 strain in contaminated crab and may have applications in food safety.

Vibrio parahaemolyticus and Vibrio vulnificus Recovered from Oysters during an Oyster Relay Study

Vibrio parahaemolyticus and Vibrio vulnificus are naturally occurring estuarine bacteria and are the leading causes of seafood-associated infections and mortality in the United States. Though multiple-antibiotic-resistant V. parahaemolyticus and V. vulnificus strains have been reported, resistance patterns in vibrios are not as well documented as those of other foodborne bacterial pathogens. Salinity relaying (SR) is a postharvest processing (PHP) treatment to reduce the abundances of these pathogens in shellfish harvested during the warmer months. The purpose of this study was to evaluate the antimicrobial susceptibility (AMS), pathogenicity, and genetic profiles of V. parahaemolyticus and V. vulnificus recovered from oysters during an oyster relay study. Isolates (V. parahaemolyticus [n = 296] and V. vulnificus [n = 94]) were recovered from oysters before and during the 21-day relaying study to detect virulence genes (tdh and trh) and genes correlated with virulence (vcgC) using multiplex quantitative PCR (qPCR). AMS to 20 different antibiotics was investigated using microbroth dilution, and pulsed-field gel electrophoresis (PFGE) was used to study the genetic profiles of the isolates. Twenty percent of V. vulnificus isolates were vcgC⁺, while 1 and 2% of V. parahaemolyticus were tdh⁺ and trh⁺, respectively. More than 77% of the V. vulnificus isolates and 30% of the V. parahaemolyticus isolates were resistant to at least one antimicrobial. Forty-eight percent of V. vulnificus and 8% of V. parahaemolyticus isolates were resistant to two or more antimicrobials. All isolates demonstrated a high genetic diversity, even among those isolated from the same site and having a similar AMS profile. No significant effects of the relaying process on AMS, virulence genes, or PFGE profiles of V. vulnificus and V. parahaemolyticus were observed.IMPORTANCE Analysis of the antibiotic resistance profiles of V. vulnificus and V. parahaemolyticus isolated from oysters during this study indicated that more than 48% of V. vulnificus isolates were resistant to two or more antimicrobials, including those recommended by the CDC for treating Vibrio infections. Also, the V. parahaemolyticus isolates showed high MICs for some of the Vibrio infection treatment antibiotics. Monitoring of AMS profiles of this bacterium is important to ensure optimal treatment of infections and improve food safety. Our study showed no significant differences in the AMS profiles of V. vulnificus (P = 0.26) and V. parahaemolyticus (P = 0.23) isolated from the oysters collected before versus after relaying. This suggests that the salinity of the relaying sites did not affect the AMS profiles of the Vibrio isolates, although it did reduce the numbers of these bacteria in oysters (S. Parveen et al., J Food Sci 82:484-491, 2017, https://doi.org/10.1111/1750-3841.13584).

A simple, portable, electrochemical biosensor to screen shellfish for Vibrio parahaemolyticus

An earlier electrochemical mechanism of DNA detection was adapted and specified for the detection of Vibrio parahaemolyticus in real samples. The reader, based on a screen printed carbon electrode, was modified with polylactide-stabilized gold nanoparticles and methylene blue was employed as the redox indicator. Detection was assessed using a microprocessor to measure current response under controlled potential. The fabricated sensor was able to specifically distinguish complementary, non-complementary and mismatched oligonucleotides. DNA was measured in the range of 2.0 × 10⁻⁸–2.0 × 10⁻¹³ M with a detection limit of 2.16 pM. The relative standard deviation for 6 replications of differential pulse voltammetry (DPV) measurement of 0.2 µM complementary DNA was 4.33%. Additionally, cross-reactivity studies against various other food-borne pathogens showed a reliably sensitive detection of the target pathogen. Successful identification of Vibrio parahaemolyticus (spiked and unspiked) in fresh cockles, combined with its simplicity and portability demonstrate the potential of the device as a practical screening tool.

Genomic Variation and Evolution of Vibrio parahaemolyticus ST36 over the Course of a Transcontinental Epidemic Expansion

Vibrio parahaemolyticus is the leading cause of seafood-related infections with illnesses undergoing a geographic expansion. In this process of expansion, the most fundamental change has been the transition from infections caused by local strains to the surge of pandemic clonal types. Pandemic clone sequence type 3 (ST3) was the only example of transcontinental spreading until 2012, when ST36 was detected outside the region where it is endemic in the U.S. Pacific Northwest causing infections along the U.S. northeast coast and Spain. Here, we used genome-wide analyses to reconstruct the evolutionary history of the V. parahaemolyticus ST36 clone over the course of its geographic expansion during the previous 25 years. The origin of this lineage was estimated to be in ~1985. By 1995, a new variant emerged in the region and quickly replaced the old clone, which has not been detected since 2000. The new Pacific Northwest (PNW) lineage was responsible for the first cases associated with this clone outside the Pacific Northwest region. After several introductions into the northeast coast, the new PNW clone differentiated into a highly dynamic group that continues to cause illness on the northeast coast of the United States. Surprisingly, the strains detected in Europe in 2012 diverged from this ancestral group around 2000 and have conserved genetic features present only in the old PNW lineage. Recombination was identified as the major driver of diversification, with some preliminary observations suggesting a trend toward a more specialized lifestyle, which may represent a critical element in the expansion of epidemics under scenarios of coastal warming.IMPORTANCEVibrio parahaemolyticus and Vibrio cholerae represent the only two instances of pandemic expansions of human pathogens originating in the marine environment. However, while the current pandemic of V. cholerae emerged more than 50 years ago, the global expansion of V. parahaemolyticus is a recent phenomenon. These modern expansions provide an exceptional opportunity to study the evolutionary process of these pathogens at first hand and gain an understanding of the mechanisms shaping the epidemic dynamics of these diseases, in particular, the emergence, dispersal, and successful introduction in new regions facilitating global spreading of infections. In this study, we used genomic analysis to examine the evolutionary divergence that has occurred over the course of the most recent transcontinental expansion of a pathogenic Vibrio, the spreading of the V. parahaemolyticus sequence type 36 clone from the region where it is endemic on the Pacific coast of North America to the east coast of the United States and finally to the west coast of Europe.

Temperature effects on the growth and survival of tdh positive Vibrio parahaemolyticus in tissues of postharvest Manila clam (Ruditapes philippinarum)

Bivalve storage at inadequate temperatures contains greater densities of Vibrio parahaemolyticus. The objective of the present study was to determine if there were any differences in growth and survival of potentially pathogenic V. parahaemolyticus (tdh positive) in relation to nonpathogenic V. parahaemolyticus (tdh-trh negative) levels in Manila clams (Ruditapes philippinarum) when exposed to different postharvest temperatures. Clams were depurated then exposed to known doses of both potential pathogenic and nonpathogenic V. parahaemolyticus for 24 h. Clams were then kept at the following temperatures corresponding to the Mediterranean summer (28 °C), winter (15 °C) and refrigeration (4 °C) for 96 h. Vibrio parahaemolyticus densities were determined at 0, 24, 48, 72 and 96 h of postharvest storage. Both isolates of V. parahaemolyticus multiplied rapidly in live clams held at 28 °C, (increase of 3 logs CFU/g at 72 h). Nonpathogenic V. parahaemolyticus in clams stored at 4 °C and 15 °C showed 1 log CFU/g and 2 log CFU/g decrease at 96 h, respectively, while no significant differences were detected for pathogenic V. parahaemolyticus at these temperatures after 96 h.

Insight Into the Origin and Evolution of the Vibrio parahaemolyticus Pandemic Strain

A strain of Vibrio parahaemolyticus that emerged in 1995 caused the first known pandemic involving this species. This strain comprises clonal autochthonous ocean-dwelling bacteria whose evolution has occurred in the ocean environment. The low sequence diversity in this population enabled the discovery of information on its origin and evolution that has been hidden in bacterial clones that have evolved over a long period. Multilocus sequencing and microarray analysis, together with phylogenetic analysis, of pandemic and pre-pandemic isolates has suggested that the founder clone was an O3:K6 non-pathogenic strain that initially acquired a toxRS/new region and subsequently acquired at least seven novel genomic islands. Sequencing and comparison of whole genomes later confirmed these early observations, and it confirmed that most of the genetic changes occurred via gene conversion involving horizontally transmitted DNA. The highly clonal population rapidly diversified, especially in terms of antigenicity, and 27 serotypes have already been reported. Comparisons of the core genomes derived from the founder clone indicate that there are only a few hundred single-nucleotide variations between isolates. However, when the whole genome is considered (the core plus non-core genome and from any clonal frame), the amount of DNA with a different clonal frame can reach up to 4.2% and the number of single-nucleotide variations can reach several hundred thousand. Altogether, these and previous observations based on multilocus sequence typing, microarray analysis, and whole-genome sequencing indicate the large contribution made by DNA with different clonal genealogy to genome diversification. The evidence also indicates that horizontal gene transfer (HGT) caused the emergence of new pathogens. Furthermore, the extent of HGT seems to depend on the vicissitudes of the life of each bacterium, as exemplified by differences in thousands of base pairs acquired by HGT among almost identical genetic isolates.

Characterization of Vibrio parahaemolyticus isolated from oysters in Korea: Resistance to various antibiotics and prevalence of virulence genes

Vibrio parahaemolyticus, found frequently in oysters, is the most prevalent gastroenteritis-causing pathogen in Korea and in several other Asian countries. This study monitored changes in the environmental parameters and occurrence of V. parahaemolyticus in oyster aquaculture sites. Of the 44 presumed V. parahaemolyticus isolates obtained, when tested against 16 antibiotics, 90.9, 86.4, and 75.0% of the 44 isolates exhibited resistance to vancomycin, ampicillin, and streptomycin, respectively. PCR analysis for the presence of the toxR gene confirmed 31 of the 44 isolates as being positive V. parahaemolyticus strains. The toxR positive isolates were tested for the presence of thermostable direct hemolysin (tdh) and tdh-related hemolysin (trh) virulence genes. Only 9.1% toxR positive isolate exhibit the trh gene and none of the isolates were tested positive for tdh. The occurrence of multi drug resistance strains in the environment could be an indication of excessive usage of antibiotics in agriculture and aquaculture fields.

Defining a Core Genome Multilocus Sequence Typing Scheme for the Global Epidemiology of Vibrio parahaemolyticus

Vibrio parahaemolyticus is an important human foodborne pathogen whose transmission is associated with the consumption of contaminated seafood, with a growing number of infections reported over recent years worldwide. A multilocus sequence typing (MLST) database for V. parahaemolyticus was created in 2008, and a large number of clones have been identified, causing severe outbreaks worldwide (sequence type 3 [ST3]), recurrent outbreaks in certain regions (e.g., ST36), or spreading to other regions where they are nonendemic (e.g., ST88 or ST189). The current MLST scheme uses sequences of 7 genes to generate an ST, which results in a powerful tool for inferring the population structure of this pathogen, although with limited resolution, especially compared to pulsed-field gel electrophoresis (PFGE). The application of whole-genome sequencing (WGS) has become routine for trace back investigations, with core genome MLST (cgMLST) analysis as one of the most straightforward ways to explore complex genomic data in an epidemiological context. Therefore, there is a need to generate a new, portable, standardized, and more advanced system that provides higher resolution and discriminatory power among V. parahaemolyticus strains using WGS data. We sequenced 92 V. parahaemolyticus genomes and used the genome of strain RIMD 2210633 as a reference (with a total of 4,832 genes) to determine which genes were suitable for establishing a V. parahaemolyticus cgMLST scheme. This analysis resulted in the identification of 2,254 suitable core genes for use in the cgMLST scheme. To evaluate the performance of this scheme, we performed a cgMLST analysis of 92 newly sequenced genomes, plus an additional 142 strains with genomes available at NCBI. cgMLST analysis was able to distinguish related and unrelated strains, including those with the same ST, clearly showing its enhanced resolution over conventional MLST analysis. It also distinguished outbreak-related from non-outbreak-related strains within the same ST. The sequences obtained from this work were deposited and are available in the public database (http://pubmlst.org/vparahaemolyticus). The application of this cgMLST scheme to the characterization of V. parahaemolyticus strains provided by different laboratories from around the world will reveal the global picture of the epidemiology, spread, and evolution of this pathogen and will become a powerful tool for outbreak investigations, allowing for the unambiguous comparison of strains with global coverage.

Pathogens of Food Animals: Sources, Characteristics, Human Risk, and Methods of Detection

Pathogens associated with food production (livestock) animals come in many forms causing a multitude of disease for humans. For the purpose of this review, these infectious agents can be divided into three broad categories: those that are associated with bacterial disease, those that are associated with viruses, and those that are parasitic in nature. The goal of this chapter is to provide the reader with an overview of the most common pathogens that cause disease in humans through exposure via the food chain and the consequence of this exposure as well as risk and detection methods. We have also included a collection of unusual pathogens that although rare have still caused disease, and their recognition is warranted in light of emerging and reemerging diseases. These provide the reader an understanding of where the next big outbreak could occur. The influence of the global economy, the movement of people, and food makes understanding production animal-associated disease paramount to being able to address new diseases as they arise.

Ecological fitness and virulence features of Vibrio parahaemolyticus in estuarine environments

Vibrio parahaemolyticus is a commonly encountered and highly successful organism in marine ecosystems. It is a fast-growing, extremely versatile copiotroph that is active over a very broad range of conditions. It frequently occurs suspended in the water column (often attached to particles or zooplankton), and is a proficient colonist of submerged surfaces. This organism is an important pathogen of animals ranging from microcrustaceans to humans and is a causative agent of seafood-associated food poisoning. This review examines specific ecological adaptations of V. parahaemolyticus, including its broad tolerances to temperature and salinity, its utilization of a wide variety of organic carbon and energy sources, and its pervasive colonization of suspended and stationary materials that contribute to its success and ubiquity in temperate and tropical estuarine ecosystems. Several virulence-related features are examined, in particular the thermostable direct hemolysin (TDH), the TDH-related hemolysin (TRH), and the type 3 secretion system, and the possible importance of these features in V. parahaemolyticus pathogenicity is explored. The impact of new and much more effective PCR primers on V. parahaemolyticus detection and our views of virulent strain abundance are also described. It is clear that strains carrying the canonical virulence genes are far more common than previously thought, which opens questions regarding the role of these genes in pathogenesis. It is also clear that virulence is an evolving feature of V. parahaemolyticus and that novel combinations of virulence factors can lead to emergent virulence in which a strain that is markedly more pathogenic evolves and propagates to produce an outbreak. The effects of global climate change on the frequency of epidemic disease, the geographic distribution of outbreaks, and the human impacts of V. parahaemolyticus are increasing and this review provides information on why this ubiquitous human pathogen has increased its footprint and its significance so dramatically.

Genetic Analysis of Vibrio parahaemolyticus O3:K6 Strains That Have Been Isolated in Mexico Since 1998

Vibrio parahaemolyticus is an important human pathogen that has been isolated worldwide from clinical cases, most of which have been associated with seafood consumption. Environmental and clinical toxigenic strains of V. parahaemolyticus that were isolated in Mexico from 1998 to 2012, including those from the only outbreak that has been reported in this country, were characterized genetically to assess the presence of the O3:K6 pandemic clone, and their genetic relationship to strains that are related to the pandemic clonal complex (CC3). Pathogenic tdh⁺ and tdh⁺/trh⁺ strains were analyzed by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Also, the entire genome of a Mexican O3:K6 strain was sequenced. Most of the strains were tdh/ORF8-positive and corresponded to the O3:K6 serotype. By PFGE and MLST, there was very close genetic relationship between ORF8/O3:K6 strains, and very high genetic diversities from non-pandemic strains. The genetic relationship is very close among O3:K6 strains that were isolated in Mexico and sequences that were available for strains in the CC3, based on the PubMLST database. The whole-genome sequence of CICESE-170 strain had high similarity with that of the reference RIMD 2210633 strain, and harbored 7 pathogenicity islands, including the 4 that denote O3:K6 pandemic strains. These results indicate that pandemic strains that have been isolated in Mexico show very close genetic relationship among them and with those isolated worldwide.

Pathogen reduction co-benefits of nutrient best management practices

Background

Many of the practices currently underway to reduce nitrogen, phosphorus, and sediment loads entering the Chesapeake Bay have also been observed to support reduction of disease-causing pathogen loadings. We quantify how implementation of these practices, proposed to meet the nutrient and sediment caps prescribed by the Total Maximum Daily Load (TMDL), could reduce pathogen loadings and provide public health co-benefits within the Chesapeake Bay system.

Methods

We used published data on the pathogen reduction potential of management practices and baseline fecal coliform loadings estimated as part of prior modeling to estimate the reduction in pathogen loadings to the mainstem Potomac River and Chesapeake Bay attributable to practices implemented as part of the TMDL. We then compare the estimates with the baseline loadings of fecal coliform loadings to estimate the total pathogen reduction potential of the TMDL.

Results

We estimate that the TMDL practices have the potential to decrease disease-causing pathogen loads from all point and non-point sources to the mainstem Potomac River and the entire Chesapeake Bay watershed by 19% and 27%, respectively. These numbers are likely to be underestimates due to data limitations that forced us to omit some practices from analysis.

Discussion

Based on known impairments and disease incidence rates, we conclude that efforts to reduce nutrients may create substantial health co-benefits by improving the safety of water-contact recreation and seafood consumption.

Host, pathogen and environment: a bacterial gbpA gene expression study in response to magnesium environment and presence of prawn carapace and commercial chitin

Background

Vibrio parahaemolyticus is a Gram-negative halophilic bacterium which is found largely in estuarine and coastal waters. The bacteria has been a main focus in gastro-intestinal infections caused primarily due to the consumption of contaminated seafood. It was shown to survive in magnesium concentrations as high as 300 mM which are toxic to various other micro-organisms. Several genes of V. parahaemolyticus were studied, among which gbpA (N-acetyl glucosamine binding protein) was reported in Vibrio cholerae.

Methods

The current study investigates the V. parahaemolyticus gbpA gene expression at different concentrations of magnesium sulfate heptahydrate (MgSO₄·7H₂O, chosen as the magnesium environment), in the presence of the host’s (prawn) carapace and the mimicked carapace [commercial chitin flakes (Sigma)]. The concentrations of MgSO₄·7H₂O utilized were approximately 0, 1, 75, 137, 225 and 300 mM. These were selected based upon the survival conditions required by prawn and bacteria, respectively. 0.05 gm/3 ml of carapace (by dry weight) and commercial chitin flakes were used in the experiments. Bacterial count was performed for the biological triplicates for the 3 experimental setups. The genome of Vibrio parahaemolyticus PCV08-7 (VPPCV08-7) was used as a reference, based on whose translated gbpA gene the probable protein-chemical interactions were determined on the STITCH database.

Results

The GbpA protein was shown to interact with chitin on the STITCH database. In our experiments, the gbpA showed lower gene expression levels at different MgSO₄·7H₂O concentrations in the presence of chitin and carapace, than with the presence of only MgSO₄•7H₂O. In addition, the bacterial count for various concentrations of magnesium used, revealed a distinct decrease in bacterial count within and among each of the three experimental setups.

Conclusion

In the presence of only magnesium, an increase in the gbpA expression with neither chitin nor carapace and vice versa supported by the results from the bacterial counts could help further studies to prove that the moulting phase of prawns may trigger increased expression of the V. parahaemolyticus gbpA gene.

Electronic supplementary material

The online version of this article (doi:10.1186/s13099-016-0105-5) contains supplementary material, which is available to authorized users.

A Nonautochthonous U.S. Strain of Vibrio parahaemolyticus Isolated from Chesapeake Bay Oysters Caused the Outbreak in Maryland in 2010

In the summer of 2010, Vibrio parahaemolyticus caused an outbreak in Maryland linked to the consumption of oysters. Strains isolated from both stool and oyster samples were indistinguishable by pulsed-field gel electrophoresis (PFGE). However, the oysters contained other potentially pathogenic V. parahaemolyticus strains exhibiting different PFGE patterns. In order to assess the identity, genetic makeup, relatedness, and potential pathogenicity of the V. parahaemolyticus strains, we sequenced 11 such strains (2 clinical strains and 9 oyster strains). We analyzed these genomes by in silico multilocus sequence typing (MLST) and determined their phylogeny using a whole-genome MLST (wgMLST) analysis. Our in silico MLST analysis identified six different sequence types (STs) (ST8, ST676, ST810, ST811, ST34, and ST768), with both of the clinical and four of the oyster strains being identified as belonging to ST8. Using wgMLST, we showed that the ST8 strains from clinical and oyster samples were nearly indistinguishable and belonged to the same outbreak, confirming that local oysters were the source of the infections. The remaining oyster strains were genetically diverse, differing in >3,000 loci from the Maryland ST8 strains. eBURST analysis comparing these strains with strains of other STs available at the V. parahaemolyticus MLST website showed that the Maryland ST8 strains belonged to a clonal complex endemic to Asia. This indicates that the ST8 isolates from clinical and oyster sources were likely not endemic to Maryland. Finally, this study demonstrates the utility of whole-genome sequencing (WGS) and associated analyses for source-tracking investigations.

IMPORTANCE

Vibrio parahaemolyticus is an important foodborne pathogen and the leading cause of bacterial infections in the United States associated with the consumption of seafood. In the summer of 2010, Vibrio parahaemolyticus caused an outbreak in Maryland linked to oyster consumption. Strains isolated from stool and oyster samples were indistinguishable by pulsed-field gel electrophoresis (PFGE). The oysters also contained other potentially pathogenic V. parahaemolyticus strains with different PFGE patterns. Since their identity, genetic makeup, relatedness, and potential pathogenicity were unknown, their genomes were determined by using next-generation sequencing. Whole-genome sequencing (WGS) analysis by whole-genome multilocus sequence typing (wgMLST) allowed (i) identification of clinical and oyster strains with matching PFGE profiles as belonging to ST8, (ii) determination of oyster strain diversity, and (iii) identification of the clinical strains as belonging to a clonal complex (CC) described only in Asia. Finally, WGS and associated analyses demonstrated their utility for trace-back investigations.

Population Relationship of Vibrio parahaemolyticus Isolates Derived from Aquaculture Ponds, a Seafood Market, Restaurants, and Clinical Samples

To study the relationship between environmental and clinical populations of Vibrio parahaemolyticus, we collected in total 86 isolates from Southern China during one and a half years. Sixty-eight isolates were recovered from aquaculture ponds, a seafood market, and restaurants, and 18 isolates were recovered from clinical samples. Virulence gene analysis revealed that 25 isolates (14 clinical and 11 environmental) tested positive for tdh, but only 4 carried trh. Interestingly, none of the tdh(+) environmental isolates was recovered from ponds. Both environmental and clinical tdh(+) isolates, except for one clinical isolate, harbor type III secretion system 2α (T3SS2α) and T3SS2β-related genes, including vopB2α, which was previously suggested to be absent from environmental strains. More than 70% of clinical isolates carried the pandemic marker of new toxRS (GS-PCR(+)), which was not present in the environmental isolates. Pulsed-field gel electrophoresis and multilocus sequence typing analysis showed a high degree of genetic diversity within the environmental isolates. In contrast, the clinical population formed a tight cluster that differed from the environmental isolates. These findings suggest that the pandemic strains of V. parahaemolyticus may not directly originate from marine animals. Rather the environments where they are maintained could serve as reservoirs for toxigenic, but not pandemic strains. These environments provide an ideal place for generation of new toxigenic strains through DNA exchange, which was revealed by extensive recombination events in recA sequences of the environmental isolates.

Host, pathogen and the environment: the case of Macrobrachium rosenbergii, Vibrio parahaemolyticus and magnesium

Macrobrachium rosenbergii is well-known as the giant freshwater prawn, and is a commercially significant source of seafood. Its production can be affected by various bacterial contaminations. Among which, the genus Vibrio shows a higher prevalence in aquatic organisms, especially M. rosenbergii, causing food-borne illnesses. Vibrio parahaemolyticus, a species of Vibrio is reported as the main causative of the early mortality syndrome. Vibrio parahaemolyticus infection in M. rosenbergii was studied previously in relation to the prawn's differentially expressed immune genes. In the current review, we will discuss the growth conditions for both V. parahaemolyticus and M. rosenbergii and highlight the role of magnesium in common, which need to be fully understood. Till date, there has not been much research on this aspect of magnesium. We postulate a model that screens a magnesium-dependent pathway which probably might take effect in connection with N-acetylglucosamine binding protein and chitin from V. parahaemolyticus and M. rosenbergii, respectively. Further studies on magnesium as an environment for V. parahaemolyticus and M. rosenbergii interaction studies will provide seafood industry with completely new strategies to employ and to avoid seafood related contaminations.

Epidemiological investigation of a foodborne outbreak in Spain associated with U.S. West Coast genotypes of Vibrio parahaemolyticus

We describe an outbreak of seafood-associated Vibrio parahaemolyticus in Galicia, Spain in on 18th of August 2012 affecting 100 of the 114 passengers travelling on a food banquet cruise boat. Epidemiological information from 65 people was available from follow-on interviews, of which 51 cases showed symptoms of illness. The food items identified through the questionnaires as the most probable source of the infections was shrimp. This product was unique in showing a statistically significant and the highest OR with a value of 7.59 (1.52-37.71). All the nine strains isolated from stool samples were identified as V. parahaemolyticus, seven were positive for both virulence markers tdh and trh, a single strain was positive for trh only and the remaining strain tested negative for both trh and tdh. This is the largest foodborne Vibrio outbreak reported in Europe linked to domestically processed seafood. Moreover, this is the first instance of strains possessing both tdh+ and trh+ being implicated in an outbreak in Europe and that a combination of strains represent several pathogenicity groups and belonging to different genetic variants were isolated from a single outbreak. Clinical isolates were associated with a novel genetic variant of V. parahaemolyticus never detected before in Europe. Further analyses demonstrated that the outbreak isolates showed indistinguishable genetic profiles with hyper-virulent strains from the Pacific Northwest, USA, suggesting a recent transcontinental spread of these strains.

Occurrence and Antibiotic Resistance of Vibrio parahaemolyticus from Shellfish in Selangor, Malaysia

High consumer demand for shellfish has led to the need for large-scale, reliable shellfish supply through aquaculture or shellfish farming. However, bacterial infections which can spread rapidly among shellfish poses a major threat to this industry. Shellfish farmers therefore often resort to extensive use of antibiotics, both prophylactically and therapeutically, in order to protect their stocks. The extensive use of antibiotics in aquaculture has been postulated to represent a major contributing factor in the rising incidence of antimicrobial resistant pathogenic bacteria in shellfish. This study aimed to investigate the incidence of pathogenic Vibrio parahaemolyticus and determine the antibiotic resistance profile as well as to perform plasmid curing in order to determine the antibiotic resistance mediation. Based on colony morphology, all 450 samples tested were positive for Vibrio sp; however, tox-R assay showed that only 44.4% (200/450) of these were V. parahaemolyticus. Out of these 200 samples, 6.5% (13/200) were trh-positive while none were tdh-positive. Antibiotic resistance was determined for all V. parahaemolyticus identified against 14 commonly used antibiotics and the multiple antibiotic resistance index (MAR) was calculated. The isolates demonstrated high resistance to several antibiotics tested- including second and third-line antibiotics- with 88% resistant to ampicillin, 81% to amikacin,70.5% to kanamycin, 73% to cefotaxime, and 51.5% to ceftazidime. The MAR index ranged from 0.00 to 0.79 with the majority of samples having an index of 0.36 (resistant to five antibiotics). Among the 13 trh-positive strains, almost 70% (9/13) demonstrated resistance to 4 or more antibiotics. Plasmid profiling for all V. parahaemolyticus isolates revealed that 86.5% (173/200) contained plasmids - ranging from 1 to 7 plasmids with DNA band sizes ranging from 1.2 kb to greater than 10 kb. 6/13 of the pathogenic V. pathogenic strains contained plasmid. After plasmid curing, the plasmid containing pathogenic strains isolated in our study have chromosomally mediated ampicillin resistance while the remaining resistance phenotypes are plasmid mediated. Overall, our results indicate that while the incidence of pathogenic V. parahaemolyticus in shellfish in Selangor still appears to be at relatively reassuring levels, antibiotic resistance is a real concern and warrants ongoing surveillance.

Prevalences of pathogenic and non-pathogenic Vibrio parahaemolyticus in mollusks from the Spanish Mediterranean Coast

Vibrio parahaemolyticus is a well-recognized pathogen of humans. To better understand the ecology of the human-pathogenic variants of this bacterium in the environment, a study on the prevalence in bivalves of pathogenic variants (tlh+ and tdh+ and/or trh+) versus a non-pathogenic one (only tlh+ as species marker for V. parahaemolyticus), was performed in two bays in Catalonia, Spain. Environmental factors that might affect dynamics of both variants of V. parahaemolyticus were taken into account. The results showed that the global prevalence of total V. parahaemolyticus found in both bays was 14.2% (207/1459). It was, however, significantly dependent on sampling point, campaign (year) and bivalve species. Pathogenic variants of V. parahaemolyticus (tdh+ and/or trh+) were detected in 3.8% of the samples (56/1459), meaning that the proportion of bivalves who contained tlh gene were contaminated by pathogenic V. parahaemolyticus strains is 27.1% (56/207). Moreover, the presence of pathogenic V. parahaemolyticus (trh+) was significantly correlated with water salinity, thus the probability of finding pathogenic V. parahaemolyticus decreased 1.45 times with every salinity unit (ppt) increased. Additionally, data showed that V. parahaemolyticus could establish close associations with Ruditapes spp. (P-value < 0.001), which could enhance the transmission of illness to human by pathogenic variants, when clams were eaten raw or slightly cooked. This study provides information on the abundance, ecology and characteristics of total and human-pathogenic V. parahaemolyticus variants associated with bivalves cultured in the Spanish Mediterranean Coast.

Influence of Environmental Factors on Vibrio spp. in Coastal Ecosystems

Various studies have examined the relationships between vibrios and the environmental conditions surrounding them. However, very few reviews have compiled these studies into cohesive points. This may be due to the fact that these studies examine different environmental parameters, use different sampling, detection, and enumeration methodologies, and occur in diverse geographic locations. The current article is one approach to compile these studies into a cohesive work that assesses the importance of environmental determinants on the abundance of vibrios in coastal ecosystems.

Temporal and Spatial Variation in the Abundance of Total and Pathogenic Vibrio parahaemolyticus in Shellfish in China

We investigated the abundance of total and pathogenic Vibrio parahaemolyticus in shellfish sampled from four provinces in China during May 2013 and March 2014 using the most probable number-polymerase chain reaction (MPN-PCR) method. Total V. parahaemolyticus was detected in 67.7% of 496 samples. A total of 38.1% and 10.1% of samples exceeded 1,000 MPN g^-1 and 10,000 MPN g^-1, respectively. V. parahaemolyticus densities followed a seasonal and geographical trend, with Guangxi and Sichuan shellfish possessing total V. parahaemolyticus levels that were 100-fold higher than those of the Liaoning and Shandong regions. Moreover, the levels of V. parahaemolyticus were at least 10-fold higher in the summer and autumn than in the cooler seasons. Pathogenic V. parahaemolyticus levels were generally lower than total V. parahaemolyticus levels by several log units and tended to be high in samples contaminated with high total V. parahaemolyticus levels. The aqua farms had a lower prevalence but higher abundance of total V. parahaemolyticus compared to retail markets. The catering markets showed the lowest levels of total V. parahaemolyticus, but 20.0% of samples exceeded 1,000 MPN g^-1. The levels of both total and pathogenic V. parahaemolyticus in oysters were higher than in clams. The log-transformed abundance of V. parahaemolyticus was significantly correlated with both water temperature and air temperature but not water salinity. These results provide baseline contamination data of V. parahaemolyticus in shellfish in China, which can be applied to local risk assessments to prioritize risk control to key sectors and evaluate the effectiveness of future control measures.

Occurrence of Vibrio parahaemolyticus, Vibrio cholerae, and Vibrio vulnificus in the Aquacultural Environments of Taiwan

The occurrence of Vibrio parahaemolyticus, Vibrio vulnificus, and Vibrio cholerae in a total of 72 samples from six aquaculture ponds for groupers, milk fish, and tilapia in southern Taiwan was examined by the membrane filtration and colony hybridization method. The halophilic V. parahaemolyticus was only recovered in seawater ponds, with a high isolation frequency of 86.1% and a mean density of 2.6 log CFU/g. V. cholerae was found in both the seawater and freshwater ponds but preferentially in freshwater ponds, with a frequency of 72.2% and a mean density of 1.65 log CFU/g. V. vulnificus was identified mainly in seawater ponds, with an isolation frequency of 27.8%. The density of V. parahaemolyticus in seawater ponds was positively related to water temperature (Pearson correlation coefficient, r = 0.555) and negatively related to salinity (r = 2 0.333). The density of V. cholerae in all six ponds was positively related to water temperature (r = 0.342) and negatively related to salinity (r = 2 0.432). Two putatively pathogenic tdh(+) V. parahaemolyticus isolates (1.4% of the samples) and no ctx(+) V. cholerae isolates were identified. The experimental results may facilitate assessments of the risk posed by these pathogenic Vibrio species in Taiwan, where aquaculture provides a large part of the seafood supply.