Vibrio bacteria in raw oysters: managing risks to human health

Virulence phenotypes differ between toxigenic Vibrio parahaemolyticus isolated from western coasts of Europe

Vibrio parahaemolyticus is the leading bacterial cause of gastroenteritis associated with seafood consumption worldwide. Not all members of the species are thought to be pathogenic, thus identification of virulent organisms is essential to protect public health and the seafood industry. Correlations of human disease and known genetic markers (e.g. thermostable direct hemolysin (TDH), TDH-related hemolysin (TRH)) appear complex. Some isolates recovered from patients lack these factors, while their presence has become increasingly noted in isolates recovered from the environment. Here, we used whole-genome sequencing in combination with mammalian and insect models of infection to assess the pathogenic potential of V. parahaemolyticus isolated from European Atlantic shellfish production areas. We found environmental V. parahaemolyticus isolates harboured multiple virulence-associated genes, including TDH and/or TRH. However, carriage of these factors did not necessarily reflect virulence in the mammalian intestine, as an isolate containing TDH and the genes coding for a type 3 secretion system (T3SS) 2α virulence determinant, appeared avirulent. Moreover, environmental V. parahaemolyticus lacking TDH or TRH could be assigned to groups causing low and high levels of mortality in insect larvae, with experiments using defined bacterial mutants showing that a functional T3SS1 contributed to larval death. When taken together, our findings highlight the genetic diversity of V. parahaemolyticus isolates found in the environment, their potential to cause disease and the need for a more systematic evaluation of virulence in diverse V. parahaemolyticus to allow better genetic markers.

Comprehensive analysis and assessment of exposure to enteric viruses and bacteria in shellfish

Shellfish species, including oysters, clams, and mussels, are extensively cultured in coastal waters. Its location is determined by factors such as nutrient availability, water temperature, tidal cycle, and the presence of contaminants such as Escherichia coli and enteric viruses. With the expansion and intensification of human activities at vicinities, the presence of anthropogenic contaminants has increased, threatening shellfish farms and consumer safety give the prevalent consumption of raw shellfish. This literature review aims to provide a comprehensive analysis of the dietary exposure and assess the risk associated with enteric viruses and bacteria detected in shellfish. The predominant bacteria and viruses detected in shellfish are reported, and the potential interrelation is discussed. The main characteristics of each contaminant and shellfish were reviewed for a more comprehensive understanding. To facilitate a direct estimation of exposure, the estimated daily intake (EDI) of bacteria was calculated based on the average levels of E. coli in shellfish, as reported in the literature. The mean daily ingestion of seafood in each of the five continents was considered. Asia exhibited the highest intake of contaminants, with an average of ±5.6 E. coli units/day.kg body weight in cockles. Simulations were conducted using recommended shellfish consumption levels established by state agencies, revealing significantly lower (p < 0.01) EDI for all continents compared to estimations based on recommended levels. This indicates a higher risk associated with healthy shellfish ingestion, potentially leading to increased intoxication incidents with a change in dietary habits. To promote a healthier lifestyle through increased shellfish consumptions, it is imperative to reduce the exposure of shellfish species to bacteria and enteric viruses. The conventional use of E. coli as the sole indicator for consumption safety and water quality in shellfish farms has been deemed insufficient. Instances where shellfish met E. coli limits established by state agencies were often found to be contaminated with human enteric viruses. Therefore, a holistic approach considering the entire production chain is necessary to support the shellfish industry and ensure food safety.

Development of Multienzyme Isothermal Rapid Amplification (MIRA) Combined with Lateral-Flow Dipstick (LFD) Assay to Detect Species-Specific tlh and Pathogenic trh and tdh Genes of Vibrio parahaemolyticus

Vibrio parahaemolyticus causes severe gastroenteritis in humans after consuming contaminated raw or undercooked seafood. A species-specific marker, the thermolabile hemolysin (tlh) gene, and two pathogenic markers, thermostable-related hemolysin (trh) and thermostable-direct hemolysin (tdh) genes, have been used to identify V. parahaemolyticus and determine its pathogenicity using both PCR and qPCR assays. To enable testing in field conditions with limited resources, this study aimed to develop a simple and rapid method to detect the species-specific (tlh) and pathogenic (trh and tdh) genes of V. parahaemolyticus using multienzyme isothermal rapid amplification (MIRA) combined with a lateral-flow dipstick (LFD). The amplification of the tlh, trh, and tdh genes could be completed within 20 min at temperatures ranging from 30 to 45 °C (p < 0.05). The test yielded positive results for V. parahaemolyticus but produced negative results for nine Vibrio species and eighteen foodborne pathogenic bacterial species. MIRA-LFD could detect 10 fg of DNA and 2 colony-forming units (CFU) of V. parahaemolyticus per reaction, demonstrating a sensitivity level comparable to that of qPCR, which can detect 10 fg of DNA and 2 CFU per reaction. Both MIRA-LFD and qPCR detected seven tlh-positive results from thirty-six oyster samples, whereas one positive result was obtained using the PCR assay. No positive results for the trh and tdh genes were obtained from any oyster samples using MIRA-LFD, PCR, and qPCR. This study suggests that MIRA-LFD is a simple and rapid method to detect species-specific and pathogenic genes of V. parahaemolyticus with high sensitivity.

Inactivation of two oyster pathogens by photocatalysis and monitoring of changes in the microbiota of seawater: A case study on Ostreid herpes virus 1 μVar and Vibrio harveyi

The pollution of seawater by both biotic (bacteria, viruses) and abiotic contaminants (biocides, pharmaceutical residues) frequently leads to economic losses in aquaculture activities mostly mortality events caused by microbial infection. Advanced Oxidation Processes (AOPs) such as heterogeneous photocatalysis allow the removal of all organic contaminants present in water and therefore could reduce production losses in land-based farms. Oysters in land-based farms such as hatcheries and nurseries suffer from a large number of mortality events, resulting in significant losses. If photocatalysis has been widely studied for the decontamination, its application for disinfection is still overlooked, especially on seawater for viruses. We therefore studied seawater disinfection using the photocatalysis (UV365/TiO2) method in the context of Pacific oyster mortality syndrome (POMS). POMS has been defined as a polymicrobial disease involving an initial viral infection with Ostreid Herpes Virus 1, accompanied by multiple bacterial infections. We investigated the impact of treatment on Vibrio harveyi, a unique opportunistic pathogenic bacterium, and on a complex microbial community reflecting a natural POMS event. Viral inactivation was monitored using experimental infections to determine whether viral particles were still infectious after. Changes in the total bacterial community in seawater were studied by comparing UV365/TiO2 treatment with UV365-irradiated seawater and untreated seawater. In the case of OsHV-1, a 2-h photocatalytic treatment prevents POMS disease and oyster mortality. The same treatment also inactivates 80% of viable Vibrio harveyi culture (c.a. 1.5 log). Since OsHV-1 and Vibrio harveyi are effectively inactivated without long-term destabilization of the total bacterial microbiota in the seawater, photocatalysis appears to be a relevant alternative for disinfecting seawater in land-based oyster beds.

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

Changing climatic conditions influence parameters associated with the growth of pathogenic Vibrio spp. in the environment and, hence, are linked to increased incidence of vibriosis. Between 1992 and 2022, a long-term increase in Vibrio spp. infections was reported in Florida, USA. Furthermore, a spike in Vibrio spp. infections was reported post Hurricane Ian, a category five storm that made landfall in Florida on 28 September 2022. During October 2022, water and oyster samples were collected from three stations in Lee County in an area significantly impacted by Ian. Vibrio spp. were isolated, and whole-genome sequencing and phylogenetic analysis were done, with a focus on Vibrio parahaemolyticus and Vibrio vulnificus to provide genetic insight into pathogenic strains circulating in the environment. Metagenomic analysis of water samples provided insight with respect to human health-related factors, notably the detection of approximately 12 pathogenic Vibrio spp., virulence and antibiotic resistance genes, and mobile genetic elements, including the SXT/R391 family of integrative conjugative elements. Environmental parameters were monitored as part of a long-term time series analysis done using satellite remote sensing. In addition to anomalous rainfall and storm surge, changes in sea surface temperature and chlorophyll concentration during and after Ian favored the growth of Vibrio spp. In conclusion, genetic analysis coupled with environmental data and remote sensing provides useful public health information and, hence, constitute a valuable tool to proactively detect and characterize environmental pathogens, notably vibrios. These data can aid the development of early warning systems by yielding a larger source of information for public health during climate change. 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.

Host and Water Microbiota Are Differentially Linked to Potential Human Pathogen Accumulation in Oysters

Oysters play an important role in coastal ecology and are a globally popular seafood source. However, their filter-feeding lifestyle enables coastal pathogens, toxins, and pollutants to accumulate in their tissues, potentially endangering human health. While pathogen concentrations in coastal waters are often linked to environmental conditions and runoff events, these do not always correlate with pathogen concentrations in oysters. Additional factors related to the microbial ecology of pathogenic bacteria and their relationship with oyster hosts likely play a role in accumulation but are poorly understood. In this study, we investigated whether microbial communities in water and oysters were linked to accumulation of Vibrio parahaemolyticus, Vibrio vulnificus, or fecal indicator bacteria. Site-specific environmental conditions significantly influenced microbial communities and potential pathogen concentrations in water. Oyster microbial communities, however, exhibited less variability in microbial community diversity and accumulation of target bacteria overall and were less impacted by environmental differences between sites. Instead, changes in specific microbial taxa in oyster and water samples, particularly in oyster digestive glands, were linked to elevated levels of potential pathogens. For example, increased levels of V. parahaemolyticus were associated with higher relative abundances of cyanobacteria, which could represent an environmental vector for Vibrio spp. transport, and with decreased relative abundance of Mycoplasma and other key members of the oyster digestive gland microbiota. These findings suggest that host and microbial factors, in addition to environmental variables, may influence pathogen accumulation in oysters. IMPORTANCE Bacteria in the marine environment cause thousands of human illnesses annually. Bivalves are a popular seafood source and are important in coastal ecology, but their ability to concentrate pathogens from the water can cause human illness, threatening seafood safety and security. To predict and prevent disease, it is critical to understand what causes pathogenic bacteria to accumulate in bivalves. In this study, we examined how environmental factors and host and water microbial communities were linked to potential human pathogen accumulation in oysters. Oyster microbial communities were more stable than water communities, and both contained the highest concentrations of Vibrio parahaemolyticus at sites with warmer temperatures and lower salinities. High oyster V. parahaemolyticus concentrations corresponded with abundant cyanobacteria, a potential vector for transmission, and a decrease in potentially beneficial oyster microbes. Our study suggests that poorly understood factors, including host and water microbiota, likely play a role in pathogen distribution and pathogen transmission.

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.

Vibrio parahaemolyticus and Vibrio vulnificus in vitro colonization on plastics influenced by temperature and strain variability

Marine bacteria often exist in biofilms as communities attached to surfaces, like plastic. Growing concerns exist regarding marine plastics acting as potential vectors of pathogenic Vibrio, especially in a changing climate. It has been generalized that Vibrio vulnificus and Vibrio parahaemolyticus often attach to plastic surfaces. Different strains of these Vibrios exist having different growth and biofilm-forming properties. This study evaluated how temperature and strain variability affect V. parahaemolyticus and V. vulnificus biofilm formation and characteristics on glass (GL), low-density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS). All strains of both species attached to GL and all plastics at 25, 30, and 35°C. As a species, V. vulnificus produced more biofilm on PS (p ≤ 0.05) compared to GL, and biofilm biomass was enhanced at 25°C compared to 30° (p ≤ 0.01) and 35°C (p ≤ 0.01). However, all individual strains' biofilm biomass and cell densities varied greatly at all temperatures tested. Comparisons of biofilm-forming strains for each species revealed a positive correlation (r = 0.58) between their dry biomass weight and OD₅₇₀ values from crystal violet staining, and total dry biofilm biomass for both species was greater (p ≤ 0.01) on plastics compared to GL. It was also found that extracellular polymeric substance (EPS) chemical characteristics were similar on all plastics of both species, with extracellular proteins mainly contributing to the composition of EPS. All strains were hydrophobic at 25, 30, and 35°C, further illustrating both species' affinity for potential attachment to plastics. Taken together, this study suggests that different strains of V. parahaemolyticus and V. vulnificus can rapidly form biofilms with high cell densities on different plastic types in vitro. However, the biofilm process is highly variable and is species-, strain-specific, and dependent on plastic type, especially under different temperatures.

Vibrio ostreae sp. nov., a novel gut bacterium isolated from a Yellow Sea oyster

A Gram-stain-negative, oxidase- and catalase-positive, facultative anaerobic motile bacterium, designated strain OG9-811^T, was isolated from the gut of an oyster collected in the Yellow Sea, Republic of Korea. The strain grew at 10-37 °C, pH 6.0-9.0 and with 0.5-10% (w/v) NaCl. Phylogenetic analysis based on the 16S rRNA gene sequences revealed that strain OG9-811^T affiliated with the genus Vibrio, with the highest sequence similarity of 98.2% to Vibrio coralliilyticus ATCC BAA-450^T followed by Vibrio variabilis R-40492^T (98.0 %), Vibrio hepatarius LMG 20362^T (97.7 %) and Vibrio neptunius LMG 20536^T (97.6 %); other relatives were Vibrio tritonius JCM 16456^T (97.4 %), Vibrio fluvialis NBRC 103150^T (97.0 %) and Vibrio furnissii CIP 102972^T (97.0 %). The complete genome of strain OG9-811^T comprised two chromosomes of a total 4 807 684 bp and the G+C content was 50.2 %. Results of analysis based on the whole genome sequence showed the distinctiveness of strain OG9-811^T. The average nucleotide identity (ANI) values between strain OG9-811^T and the closest strains V. coralliilyticus ATCC BAA-450^T, V. variabilis R-40492^T, V. hepatarius LMG 20362^T, V. neptunius KCTC 12702^T , V. tritonius JCM 16456^T, V. fluvialis ATCC 33809^T and V. furnissi CIP 102972^T were 73.0, 72.6, 73.3, 73.0, 72.7, 78.5 and 77.8 %, respectively, while the digital DNA-DNA hybridization values between strain OG9-811^T and the above closely related strains were 20.8, 21.2, 20.8, 21.7, 20.7, 23.2 and 22.4 %, respectively. The major fatty acids of strain OG9-811^T were summed feature 3 (C_16:1 ω7c and/or C_16:1 ω6c), summed feature 8 (C_18:1 ω6c and/or C_18:1 ω7c) and C_16:0. The polar lipids contained phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol. Strain OG9-811^T contained Q-8 as a quinone. On the basis of polyphasic taxonomic characteristics, strain OG9-811^T is considered to represent a novel species, for which the name Vibrio ostreae sp. nov. is proposed. The type strain is OG9-811^T (=KCTC 72623^T=GDMCC 1.2610^T).

Characterization and Genomic Analysis of ssDNA Vibriophage vB_VpaM_PG19 within Microviridae, Representing a Novel Viral Genus

Vibrio parahaemolyticus, a widespread marine bacterium, is responsible for a variety of diseases in marine organisms. Consumption of raw or undercooked seafood contaminated with V. parahaemolyticus is also known to cause acute gastroenteritis in humans. While numerous dsDNA vibriophages have been isolated so far, there have been few studies of vibriophages belonging to the ssDNA Microviridae family. In this study, a novel ssDNA phage, vB_VpaM_PG19 infecting V. parahaemolyticus, with a 5,572 bp ssDNA genome with a G+C content of 41.31% and encoded eight open reading frames, was isolated. Genome-wide phylogenetic analysis of the total phage isolates in the GenBank database revealed that vB_VpaM_PG19 was only related to the recently deposited vibriophage vB_VpP_WS1. The genome-wide average nucleotide homology of the two phages was 89.67%. The phylogenetic tree and network analysis showed that vB_VpaM_PG19 was different from other members of the Microviridae family and might represent a novel viral genus, together with vibriophage vB_VpP_WS1, named Vimicrovirus. One-step growth curves showed that vB_VpaM_PG19 has a short incubation period, suggesting its potential as an antimicrobial agent for pathogenic V. parahaemolyticus. IMPORTANCE Vibriophage vB_VpaM_PG19 was distant from other isolated microviruses in the phylogenetic tree and network analysis and represents a novel microviral genus, named Vimicrovirus. Our report describes the genomic and phylogenetic features of vB_VpaM_PG19 and provides a potential antimicrobial candidate for pathogenic V. parahaemolyticus.

Development of a Controlled Laboratory-scale Inoculation System to Study Vibrio parahaemolyticus-oyster Interactions

Prevalence of seafood-borne gastroenteritis caused by the human pathogen Vibrio parahaemolyticus is increasing globally despite current preventative measures. The United States Centers for Disease Control have designated V. parahaemolyticus as a reportable emerging human pathogen. The Eastern oyster (Crassostrea virginica) is a natural reservoir of the bacterium in marine environments, but little is actually known regarding interactions between oysters and V. parahaemolyticus. Therefore, a laboratory-scale Biosafety Level-2 (BSL2) inoculation system was developed wherein Chesapeake Bay region oysters harvested during summer or winter months, were exposed to the clinical RIMD2210633 strain carrying a chloramphenicol-selective marker (VP RIMDmC). Homogenized whole oyster tissues were spread on selective and differential agar medium to measure viable VP RIMDmC levels. Endogenous Vibrio spp. cell numbers were significantly reduced followed chloramphenicol treatment and this likely contributed to higher VP RIMDmC oyster-associated levels, especially using winter-harvested animals. Summer-harvested oysters had significantly higher existing Vibrio levels and a lower level of artificial oyster-associated VP RIMDmC. Thus, the pre-existing microbiome appears to afford some protection from an external V. parahaemolyticus challenge. Overall, this system successfully enabled controlled manipulation of parameters influencing V. parahaemolyticus-oyster interactions and will be useful in safely testing additional pertinent environmental variables and potential mitigation strategies.

Invasive slipper limpets (Crepidula fornicata) act like a sink, rather than source, of Vibrio spp

A large knowledge gap exists regarding the disease profile and pathologic condition of the invasive, slipper limpet Crepidula fornicata. To help address this, we performed a year-long health survey at two sites in South Wales, UK – subtidal Swansea Bay and intertidal Milford Haven. In total, 1,800 limpets were screened systematically for haemolymph bacterial burdens using both general and vibrio-selective growth media (TSA + 2% NaCl and TCBS, respectively), haemolymph (blood) inspection using microscopy, a PCR-based assay targeting Vibrio spp., and multi-tissue histology. Over 99% of haemolymph samples contained cultivable bacterial colony-forming units, and 83% of limpets tested positive for the presence of vibrios via PCR (confirmed via Sanger sequencing). Vibrio presence did not vary greatly between sites, yet a strong seasonal effect was observed with significantly higher bacterial loads during the summer. Binomial logistic regression models revealed larger (older) limpets were more likely to harbour vibrios, and the growth of bacteria on TCBS was a key predictor for PCR-based vibrio detection. Histological assessment of > 340 animals revealed little evidence of inflammation, sepsis or immune reactivity despite the gross bacterial numbers. We contend that slipper limpets are not highly susceptible to bacteriosis at either site, and do not harbour vibrios known to be pathogenic to humans. The lack of susceptibility to local pathogenic bacteria may explain, in part, the invasion success of C. fornicata across this region.

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.

Antibiogram signatures of Vibrio species recovered from surface waters in South Western districts of Uganda: Implications for environmental pollution and infection control

Reports of vibriosis and other related gastrointestinal infections have remained a recurring concern in the diverse global continent. The safety of drinking surface water and associated environmental pollution has remained a public health concern in limited resource sittings. Seen in this light, we report the antibiogram signatures of Vibrio species recovered from surface waters in the South-Western districts of Uganda. Surface water samples were collected for four months for Vibrio species isolation in four districts (Bushenyi-B, Mitooma-M, Rubirizi-R, and Sheema-S) using bacteria culture procedures, disc diffusion and Polymerase Chain Reaction (PCR) technique. Isolates were characterised, and the antibiotic fingerprints were determined using PCR and nine selected antibiotics in routine use. A total of 392 Vibrio species were confirmed from the various districts (B: 172, M: 79. R: 60, S: 81), with 163 (94.77%) resistant to colistin (polymixin), 145 (84.3%) resistant to cefotaxime, 127 (73.84%) resistant to azithromycin, and 33 (19.19%) resistant to chloramphenicol among Bushenyi isolates. A similar high resistance to fluoroquinolones and carbapenem antibiotics were also recorded in other districts of the study area. A complete multiple antibiotic resistance phenotype ((M)ARPs) to the applied antibiotics (A-CTX-CXM-MEM-ATH-K-TM-C-PB-NI-CIP-NA) were also recorded among some isolates, which produced multiple antibiotic resistance indexes of 1, suggesting a high-risk source of contamination due to the usage of several antibiotics. The PCR reports also confirm ampC gene {20 (10.9%)}, beta-lactamase TEM gene (blaTEM2), {30 (10%)} and dihydropteroate synthase type-1 and 11 gene (sul 1 & 11) {16 (8%)}. The results present an implicated environmental pollution problem and a potential concern to public health, therefore there is the need for control of such infectious bacteria and environmental pollution monitoring. Hence, it is recommended various approaches crucial to monitoring of emerging trends in drug resistance at the local and international levels.

Mapping the Green-Lipped Mussel (Perna canaliculus) Microbiome: A Multi-Tissue Analysis of Bacterial and Fungal Diversity

Poor health and mortality events of the commercially important and endemic New Zealand green-lipped mussel (Perna canaliculus) pose a threat to its industry. Despite the known importance of microbiomes to animal health and environmental resilience, the host-associated microbiome is unexplored in this species. We conducted the first baseline characterization of bacteria and fungi within key host tissues (gills, haemolymph, digestive gland, and stomach) using high-throughput amplicon sequencing of 16S rRNA gene and ITS1 region for bacteria and fungi, respectively. Tissue types displayed distinctive bacterial profiles, consistent among individuals, that were dominated by phyla which reflect (1) a fluid exchange between the circulatory system (gills and haemolymph) and surrounding aqueous environment and (2) a highly diverse digestive system (digestive gland and stomach) microbiota. Gammaproteobacteria and Campylobacterota were mostly identified in the gill tissue and haemolymph, and were also found in high abundance in seawater. Digestive gland and stomach tissues were dominated by common gut bacterial phyla, such as Firmicutes, Cyanobacteria, Proteobacteria, and Bacteroidota, which reflects the selectivity of the digestive system and food-based influences. Other major notable taxa included the family Spirochaetaceae, and genera Endozoicomonas, Psychrilyobacter, Moritella and Poseidonibacter, which were highly variable among tissue types and samples. More than 50% of fungal amplicon sequence variants (ASVs) were unclassified beyond the phylum level, which reflects the lack of studies with marine fungi. However, the majority of those identified were assigned to the phylum Ascomycota. The findings from this work provide the first insight into healthy tissue microbiomes of P. canaliculus and is of central importance to understanding the effect of environmental changes on farmed mussels at the microbial level.

Microbiological Quality and Heavy Metal Concentrations in Slipper Oyster (Crassostrea iredalei) Cultured in Major Growing Areas in Capiz Province, Western Visayas, Philippines: Compliance with International Shellfish Safety and Sanitation Standards

ABSTRACT

The increasing demand for slipper oyster (Crassostrea iredalei) has propelled farmers to expand oyster cultivation areas in the Philippines, chiefly for local consumption and feasibly for export overseas. As filter feeders, oysters can accumulate pathogens from the surrounding waters, and these pathogens can cause foodborne diseases in consumers. Therefore, oyster farming areas must be monitored for microbiological quality and heavy metal concentrations. In the present study, the microbiological quality of oysters and their growing waters in the major oyster farming areas of the Cogon and Palina Rivers and Cabugao Bay (in Roxas City and the Municipality of Ivisan, respectively, Capiz Province, Western Visayas, Philippines) were examined monthly during the wet (May to October) and dry (November to April) seasons over 12 months. Regardless of the sampling period, high levels of fecal coliforms in the water and Escherichia coli in oysters were found, clearly illustrating that these oyster growing areas would meet only the class B standard under the European Union classification system and would be considered "prohibited" for growing oysters under the U.S. classification system. Although Salmonella was occasionally detected in oysters, Vibrio cholerae was not detected and Vibrio parahaemolyticus was within acceptable limits. The heavy metal concentrations in oyster meat were also determined during the wet (July) and dry (March) seasons. Zinc and copper were the most abundant metals detected, and concentrations of lead, cadmium, mercury, and chromium were below the regulatory limits set by the European Union and the U.S. Food and Drug Administration. These oyster culture areas should be rehabilitated immediately to improve the microbiological quality of the oysters. Oysters harvested from these sites must be depurated or relayed to ensure quality and safety.

HIGHLIGHTS

Fis Connects Two Sensory Pathways, Quorum Sensing and Surface Sensing, to Control Motility in Vibrio parahaemolyticus

Factor for inversion stimulation (Fis) is a global regulator that is highly expressed during exponential phase growth and undetectable in stationary phase growth. Quorum sensing (QS) is a global regulatory mechanism that controls gene expression in response to changes in cell density and growth phase. In Vibrio parahaemolyticus, a marine species and a significant human pathogen, the QS regulatory sRNAs, Qrr1 to Qrr5, are expressed during exponential growth and negatively regulate the high cell density QS master regulator OpaR. OpaR is a positive regulator of capsule polysaccharide (CPS) formation, which is required for biofilm formation, and is a repressor of lateral flagella required for swarming motility. In V. parahaemolyticus, we show that Fis is a positive regulator of the qrr sRNAs expression. In an in-frame fis deletion mutant, qrr expression was repressed and opaR expression was induced. The Δfis mutant produced CPS and biofilm, but swarming motility was abolished. Also, the fis deletion mutant was more sensitive to polymyxin B. Swarming motility requires expression of both the surface sensing scrABC operon and lateral flagella laf operon. Our data showed that in the Δfis mutant both laf and scrABC genes were repressed. Fis controlled swarming motility indirectly through the QS pathway and directly through the surface sensing pathway. To determine the effects of Fis on cellular metabolism, we performed in vitro growth competition assays, and found that Δfis was outcompeted by wild type in minimal media supplemented with intestinal mucus as a sole nutrient source. The data showed that Fis positively modulated mucus components L-arabinose, D-gluconate and N-acetyl-D-glucosamine catabolism gene expression. In an in vivo colonization competition assay, Δfis was outcompeted by wild type, indicating Fis is required for fitness. Overall, these data demonstrate a global regulatory role for Fis in V. parahaemolyticus that includes QS, motility, and metabolism.

Assessing the Bacterial Community Composition of Bivalve Mollusks Collected in Aquaculture Farms and Respective Susceptibility to Antibiotics

Aquaculture is a growing sector, providing several products for human consumption, and it is therefore important to guarantee its quality and safety. This study aimed to contribute to the knowledge of bacterial composition of Crassostrea gigas, Mytilus spp. and Ruditapes decussatus, and the antibiotic resistances/resistance genes present in aquaculture environments. Two hundred and twenty-two bacterial strains were recovered from all bivalve mollusks samples belonging to the Aeromonadaceae, Bacillaceae, Comamonadaceae, Enterobacteriaceae, Enterococcaceae, Micrococcaceae, Moraxellaceae, Morganellaceae, Pseudomonadaceae, Shewanellaceae, Staphylococcaceae, Streptococcaceae, Vibrionaceae, and Yersiniaceae families. Decreased susceptibility to oxytetracycline prevails in all bivalve species, aquaculture farms and seasons. Decreased susceptibilities to amoxicillin, amoxicillin/clavulanic acid, cefotaxime, cefoxitin, ceftazidime, chloramphenicol, florfenicol, colistin, ciprofloxacin, flumequine, nalidixic acid and trimethoprim/sulfamethoxazole were also found. This study detected six qnrA genes among Shewanella algae, ten qnrB genes among Citrobacter spp. and Escherichia coli, three oqxAB genes from Raoultella ornithinolytica and bla_TEM-1 in eight E. coli strains harboring a qnrB19 gene. Our results suggest that the bacteria and antibiotic resistances/resistance genes present in bivalve mollusks depend on several factors, such as host species and respective life stage, bacterial family, farm’s location and season, and that is important to study each aquaculture farm individually to implement the most suitable measures to prevent outbreaks.

Biochemical responses of oysters in evaluating environmental quality of tropical Indian estuarine systems

Impact of varying concentrations and counts of toxic metals and indigenous bacteria on antioxidative defense system in edible oyster, Saccostrea cucullata, collected from four tropical estuarine systems of Goa (west coast of India), are presented in this study. Relatively high abundance of bacteria was estimated from the oysters especially during monsoon season (June-September). Density of total and fecal coliforms were about 24 times higher in the organism than the surrounding water (average TC: 4360 and FC: 3475 MPN 100 ml^-1). Sedimentary Cd, Pb, and Hg concentrations varied from 0.12 to 0.48, 19.28-102.48, and 0.03-0.13 mg kg^-1 (dry wt.) while, bioaccumulation of Cd, Pb, and Hg in the oysters ranged from 5.17 to 10.6, 0.18-7.99, and 0.06-0.22 mg kg^-1 (dry wt.) respectively. Higher degree of pollution and moderate ecotoxicological risks with increasing toxicity (36-37%) was observed in two of the tropical estuaries. Biomarker response in the oysters was somewhat inconsistent with pollution load in the estuarine systems. Elevated environmental stress was observed during pre-monsoon (March-May) followed by the monsoon period. Sedimentary metals were identified as predominant inducers of antioxidative defence system in oysters from the study areas. This study suggests that, biomarker can be useful in assessing the combined effects of metal and bacterial contaminations on native oysters and in evaluating environmental quality in tropical estuarine systems.

Microbial Profiles of Retail Pacific Oysters (Crassostrea gigas) From Guangdong Province, China

Oysters are one of the main aquatic products sold in coastal areas worldwide and are popular among consumers because of their delicious taste and nutritional value. However, the microorganisms present in oysters may pose health risks to consumers. In this study, the microbial communities of Pacific oysters (Crassostrea gigas) collected from aquatic product markets in three cities (Guangzhou, Zhuhai, and Jiangmen) of Guangdong Province, China, where raw oysters are popular, were investigated. The plate counts of viable bacteria in oysters collected in the three cities were all approximately 2 log colony-forming units/g. High-throughput sequencing analysis of the V3–V4 region of the 16Sribosomal DNA gene showed a high level of microbial diversity in oysters, as evidenced by both alpha and beta diversity analysis. Proteobacteria, Bacteroidetes, and Firmicutes were the dominant phyla of the microorganisms present in these samples. A variety of pathogenic bacteria, including the fatal foodborne pathogen Vibrio vulnificus, were found, and Vibrio was the dominant genus. Additionally, the relationship between other microbial species and pathogenic microorganisms may be mostly symbiotic in oysters. These data provide insights into the microbial communities of retail oysters in the Guangdong region and indicate a considerable risk related to the consumption of raw oysters.

Reduced virulence of the MARTX toxin increases the persistence of outbreak-associated Vibrio vulnificus in host reservoirs

Opportunistic bacteria strategically dampen their virulence to allow them to survive and propagate in hosts. However, the molecular mechanisms underlying virulence control are not clearly understood. Here, we found that the opportunistic pathogen Vibrio vulnificus biotype 3, which caused an outbreak of severe wound and intestinal infections associated with farmed tilapia, secretes significantly less virulent multifunctional autoprocessing repeats-in-toxin (MARTX) toxin, which is the most critical virulence factor in other clinical Vibrio strains. The biotype 3 MARTX toxin contains a cysteine protease domain (CPD) evolutionarily retaining a unique autocleavage site and a distinct β-flap region. CPD autoproteolytic activity is attenuated following its autocleavage because of the β-flap region. This β-flap blocks the active site, disabling further autoproteolytic processing and release of the modularly structured effector domains within the toxin. Expression of this altered CPD consequently results in attenuated release of effectors by the toxin and significantly reduces the virulence of V. vulnificus biotype 3 in cells and in mice. Bioinformatic analysis revealed that this virulence mechanism is shared in all biotype 3 strains. Thus, these data provide new insights into the mechanisms by which opportunistic bacteria persist in an environmental reservoir, prolonging the potential to cause outbreaks.

Effect of Seawater Temperature Increase on the Occurrence of Coastal Vibrio vulnificus Cases: Korean National Surveillance Data from 2003 to 2016

The purpose of this study was to assess the association between seawater temperature and Vibrio vulnificus cases in coastal regions of Korea. All V. vulnificus cases in coastal regions notified to the Korea Disease Control and Prevention Agency between 2003 and 2016 were included in this work. Data for seawater temperature on the south, west, and east coast during the study period were provided by the Korea Oceanographic Data Center of the National Institute of Fisheries Science. We used a generalized additive model and performed a negative binomial regression analysis. In total, 383 notified cases were analyzed (west coast: 196 cases, south coast: 162, and east coast: 25). The maximum seawater temperature was the most significant predictor of V. vulnificus cases on the south and east coasts (relative risk according to the 1 °C increase in seawater temperature (RR) = 1.35 (95% confidence interval (CI): 1.19–1.53) and 1.30 (95% CI: 1.06–1.59), respectively). However, the mean seawater temperature was the most significant predictor for the west coast (RR = 1.34 (95% CI: 1.20–1.51)). These results indicate that continuously monitoring seawater temperature increase in each coastal area is crucial to prevent V. vulnificus infections and protect high-risk groups, such as persons with liver disease.

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.

A case-control analysis of traceback investigations for Vibrio parahaemolyticus infections (vibriosis) and pre-harvest environmental conditions in Washington State, 2013-2018

BACKGROUND

Vibrio parahaemolyticus is a major cause of seafood-borne illness. It is naturally prevalent in brackish waters and accumulates in shellfish. Vibriosis cases are rising globally, likely due to rising temperatures.

OBJECTIVES

To identify associations between vibriosis in Washington State and pre-harvest environmental and V. parahaemolyticus genetic measurements sampled from shellfish.

METHODS

Successful vibriosis traceback investigations were spatiotemporally matched to routine intertidal oyster (Crassostrea gigas) sampling events, which included measurements of temperature, salinity, and V. parahaemolyticus genetic targets (thermolabile hemolysin: tlh; thermostable direct hemolysin: tdh; thermostable direct-related hemolysin: trh). Unmatched sampling events were treated as controls. Associations were evaluated using logistic regression models.

RESULTS

Systematic differences were observed across Washington harvesting zones. These included positive associations between the odds of vibriosis and all three genetic targets in South Puget Sound, with a large odds ratio (OR) = 13.0 (95% CI: 1.5, 115.0) for a 1-log₁₀ increase in tdh when total bacterium abundance was low (tlh < 1 log₁₀ MPN/g). A positive association also occurred for a 1 °C increase in tissue temperature OR = 1.20 (95% CI: 1.10, 1.30) while a negative association occurred for a similar increase in water temperature OR = 0.70 (95% CI: 0.59, 0.81). In contrast, the coastal bays displayed positive associations for water temperature OR = 2.16 (95% CI, 1.15, 4.05), and for a 1-log₁₀ increase in the tdh:trh ratio OR = 5.85 (95% CI, 1.06, 32.26).

DISCUSSION

The zonal variation in associations indicates unique pathogenic strain prominence, suggesting tdh+/trh+ strains in South Puget Sound, such as the O4:K12 serotype, and tdh+/trh- strains in the coastal bays. The temperature discrepancy between water and oyster tissue suggests that South Puget Sound pathogenic strains flourish with exposure to relatively warm air during low tide. These findings identify new ecological risk factors for vibriosis in Washington State that can be used in future prevention efforts.

A systematic review of post-harvest interventions for Vibrio parahaemolyticus in raw oysters

BACKGROUND

Non-cholera Vibrio bacteria are a major cause of foodborne illness in the United States. Raw oysters are commonly implicated in gastroenteritis caused by pathogenic Vibrio parahaemolyticus. In response to outbreaks in 1997-1998, the US Food and Drug Administration developed a nation-wide quantitative microbial risk assessment (QMRA) of V. parahaemolyticus in raw oysters in 2005. The QMRA identified information gaps that new research may address. Incidence of sporadic V. parahaemolyticus illness has recently increased and, as oyster consumption increases and sea temperatures rise, V. parahaemolyticus outbreaks may become more frequent, posing health concerns. Updated and region-specific QMRAs will improve the accuracy and precision of risk of infection estimates.

OBJECTIVES

We identify research to support an updated QMRA of V. parahaemolyticus from oysters harvested in Chesapeake Bay and Puget Sound, focusing on observational and experimental research on post-harvest practices (PHPs) published from 2004 to 2019.

METHODS

A predefined search strategy was applied to PubMed, Embase, Scopus, Science.gov, NAL Agricola, and Google Scholar. Study eligibility criteria were defined using a population, intervention, comparator, and outcome statement. Reviewers independently coded abstracts for inclusion/exclusion using predefined criteria. Data were extracted and study quality and relevance evaluated based on published guidance for food safety risk assessments. Findings were synthesized using a weight of evidence approach.

RESULTS

Of 12,174 articles retrieved, 93 were included for full-text review. Twenty-seven studies were found to be high quality and high relevance, including studies on cold storage, high hydrostatic pressure, depuration, and disinfectant, and other PHPs. High hydrostatic pressure consistently emerged as the most effective PHP in reducing abundance of V. parahaemolyticus.

DISCUSSION

Limitations of the knowledge base and review approach involve the type and quantity of data reported. Future research should focus on PHPs for which few or no high quality and high relevance studies exist, such as irradiation and relaying.

A Fatal Case of Bacteremia Caused by Vibrio cholerae Non-O1/O139

Vibrio cholerae is a pathogen known to cause the waterborne epidemic disease cholera. Overall, V. cholerae O1 or O139 strains produce the cholera toxin that cause gastroenteritis, resulting in watery diarrhea. Most of the enterocolitis caused by V. cholerae can be easily treated with fluid therapy and conservative care. However, V. cholerae non-O1/O139 strains can cause extraintestinal infections, such as wound infection or sepsis, in immunocompromised patients. The clinical course of these infections is very similar to that of V. vulnificus infection. We report about a 52-year-old man without previous underlying disease who was diagnosed with V. cholerae non-O1/O139 infection and died within 72 hours after admission to the intensive care unit.

Phages as a Cohesive Prophylactic and Therapeutic Approach in Aquaculture Systems

Facing antibiotic resistance has provoked a continuously growing focus on phage therapy. Although the greatest emphasis has always been placed on phage treatment in humans, behind phage application lies a complex approach that can be usefully adopted by the food industry, from hatcheries and croplands to ready-to-eat products. Such diverse businesses require an efficient method for combating highly pathogenic bacteria since antibiotic resistance concerns every aspect of human life. Despite the vast abundance of phages on Earth, the aquatic environment has been considered their most natural habitat. Water favors multidirectional Brownian motion and increases the possibility of contact between phage particles and their bacterial hosts. As the global production of aquatic organisms has rapidly grown over the past decades, phage treatment of bacterial infections seems to be an obvious and promising solution in this market sector. Pathogenic bacteria, such as Aeromonas and Vibrio, have already proved to be responsible for mass mortalities in aquatic systems, resulting in economic losses. The main objective of this work is to summarize, from a scientific and industry perspective, the recent data regarding phage application in the form of targeted probiotics and therapeutic agents in aquaculture niches.

Heat treatments of peptides from oyster (Crassostrea gigas) and the impact on their digestibility and angiotensin I converting enzyme inhibitory activity

The changes of protein digestibility, the peptides in the digestive juice and angiotensin I converting enzyme (ACE) inhibitory activity after heating of oysters were investigated. The digestibility of raw oysters was 71.1%, and that of oysters heated at 100 °C was 67.9%. A total of 169 and 370 peptides were identified from the digestion of raw oysters and heated oysters, respectively. According to UPLC-Q-TOF-MS spectra, the peptides with a molecular weight below 2000 Da accounted for 87.6% of the total peptides of raw oysters and 94% of heated oysters. Testing the ACE inhibitory activity in vitro, the IC₅₀ values of raw oyster and cooked oyster were 6.77 μg/mL and 3.34 μg/mL, respectively. Taken together, the results showed that heated oysters could produce more active peptides and provide ACE inhibitory activity.

Vibrio-bivalve interactions in health and disease

In the marine environment, bivalve mollusks constitute habitats for bacteria of the Vibrionaceae family. Vibrios belong to the microbiota of healthy oysters and mussels, which have the ability to concentrate bacteria in their tissues and body fluids, including the hemolymph. Remarkably, these important aquaculture species respond differently to infectious diseases. While oysters are the subject of recurrent mass mortalities at different life stages, mussels appear rather resistant to infections. Thus, Vibrio species are associated with the main diseases affecting the worldwide oyster production. Here, we review the current knowledge on Vibrio-bivalve interaction in oysters (Crassostrea sp.) and mussels (Mytilus sp.). We discuss the transient versus stable associations of vibrios with their bivalve hosts as well as technical issues limiting the monitoring of these bacteria in bivalve health and disease. Based on the current knowledge of oyster/mussel immunity and their interactions with Vibrio species pathogenic for oyster, we discuss how differences in immune effectors could contribute to the higher resistance of mussels to infections. Finally, we review the multiple strategies evolved by pathogenic vibrios to circumvent the potent immune defences of bivalves and how key virulence mechanisms could have been positively or negatively selected in the marine environment through interactions with predators.

Managing the risk of Vibrio parahaemolyticus infections associated with oyster consumption: A review

Vibrio parahaemolyticus is a Gram-negative bacterium that is naturally present in the marine environment. Oysters, which are water filter feeders, may accumulate this pathogen in their soft tissues, thus increasing the risk of V. parahaemolyticus infection among people who consume oysters. In this review, factors affecting V. parahaemolyticus accumulation in oysters, the route of the pathogen from primary production to consumption, and the potential effects of climate change were discussed. In addition, intervention strategies for reducing accumulation of V. parahaemolyticus in oysters were presented. A literature review revealed the following information relevant to the present study: (a) managing the safety of oysters (for human consumption) from primary production to consumption remains a challenge, (b) there are multiple factors that influence the concentration of V. parahaemolyticus in oysters from primary production to consumption, (c) climate change could possibly affect the safety of oysters, both directly and indirectly, placing public health at risk, (d) many intervention strategies have been developed to control and/or reduce the concentration of V. parahaemolyticus in oysters to acceptable levels, but most of them are mainly focused on the downstream steps of the oyster supply chain, and (c) although available regulation and/or guidelines governing the safety of oyster consumption are mostly available in developed countries, limited food safety information is available in developing countries. The information provided in this review may serve as an early warning for managing the future effects of climate change on the safety of oyster consumption.

Modeling Pathogen Dispersal in Marine Fish and Shellfish

In marine ecosystems, oceanographic processes often govern host contacts with infectious agents. Consequently, many approaches developed to quantify pathogen dispersal in terrestrial ecosystems have limited use in the marine context. Recent applications in marine disease modeling demonstrate that physical oceanographic models coupled with biological models of infectious agents can characterize dispersal networks of pathogens in marine ecosystems. Biophysical modeling has been used over the past two decades to model larval dispersion but has only recently been utilized in marine epidemiology. In this review, we describe how biophysical models function and how they can be used to measure connectivity of infectious agents between sites, test hypotheses regarding pathogen dispersal, and quantify patterns of pathogen spread, focusing on fish and shellfish pathogens.

RRSP and RID Effector Domains Dominate the Virulence Impact of Vibrio vulnificus MARTX Toxin

BACKGROUND

The bacterial pathogen Vibrio vulnificus causes severe septic foodborne infections. The multifunctional autoprocessing repeats-in-toxins (MARTX) toxin is an important secreted virulence factor. The effector domain region is essential for lethal intestinal infection in mice, but the contribution of each of the 5 effector domains to infection has not been investigated.

METHODS

V. vulnificus mutants with varying effector domain content were inoculated intragastrically to mice, and the time to death was monitored to establish the contribution of each effector domain to overall virulence. Each strain was also tested for bacterial dissemination from the intestine to internal organs and for inhibition of phagocytosis.

RESULTS

The effector domain region was required for V. vulnificus to inhibit phagocytosis by J774 macrophages, but no single effector domain was required. No single MARTX effector domain was necessary for bacterial dissemination. Nonetheless, overall survival of infected mice differed with respect to the infecting V. vulnificus strain. Removal of rid or rrsp significantly reduced the virulence potential of V. vulnificus, while deletion of duf1 or abh accelerated the time to death.

CONCLUSION

Rho GTPases inactivation domain and Ras/Rap1-specific endopeptidase each exert greater effects on virulence than other MARTX domains, suggesting that modulation of the Rho/Ras family of GTPases is a critical function of the toxin during intestinal infection.

Enteric viruses, somatic coliphages and Vibrio species in marine bathing and non-bathing waters in Italy

Microbial safety of recreational waters is a significant public health issue. In this study we assessed the occurrence and quantity of enteric viruses in bathing and non-bathing waters in Italy, in parallel with microbial faecal indicators, somatic coliphages and Vibrio spp. Enteric viruses (aichivirus, norovirus and enterovirus) were detected in 55% of bathing water samples, including samples with bacterial indicator concentrations compliant with the European bathing water Directive. Aichivirus was the most frequent and abundant virus. Adenovirus was detected only in non-bathing waters. Somatic coliphages were identified in 50% bathing water samples, 80% of which showed simultaneous presence of viruses. Vibrio species were ubiquitous, with 9 species identified, including potential pathogens (V. cholerae, V. parahaemoylticus and V. vulnificus). This is the first study showing the occurrence and high concentration of Aichivirus in bathing waters and provides original information, useful in view of a future revision of the European Directive.

Forecasting Seasonal Vibrio parahaemolyticus Concentrations in New England Shellfish

Seafood-borne Vibrio parahaemolyticus illness is a global public health issue facing resource managers and the seafood industry. The recent increase in shellfish-borne illnesses in the Northeast United States has resulted in the application of intensive management practices based on a limited understanding of when and where risks are present. We aim to determine the contribution of factors that affect V. parahaemolyticus concentrations in oysters (Crassostrea virginica) using ten years of surveillance data for environmental and climate conditions in the Great Bay Estuary of New Hampshire from 2007 to 2016. A time series analysis was applied to analyze V. parahaemolyticus concentrations and local environmental predictors and develop predictive models. Whereas many environmental variables correlated with V. parahaemolyticus concentrations, only a few retained significance in capturing trends, seasonality and data variability. The optimal predictive model contained water temperature and pH, photoperiod, and the calendar day of study. The model enabled relatively accurate seasonality-based prediction of V. parahaemolyticus concentrations for 2014–2016 based on the 2007–2013 dataset and captured the increasing trend in extreme values of V. parahaemolyticus concentrations. The developed method enables the informative tracking of V. parahaemolyticus concentrations in coastal ecosystems and presents a useful platform for developing area-specific risk forecasting models.

Snapshot of environmental condition in different tropical estuarine systems by using S. cucullata (an edible oyster) as bio-indicator

Accumulation of toxic metals and indigenous bacteria in oyster, (Saccostrea cucullata) and their impact on antioxidant enzyme activities in the biological system was studied and used to provide snapshot of environmental condition in different tropical estuarine systems. The sedimentary Cd, Pb, and Hg concentration varied from 0.1 to 1.8, 22.0 to 98.0, and 0.03 to 0.11 mg kg^-1 (dry wt.) respectively. The bioaccumulated Cd, Pb, and Hg concentration in the oysters ranged from 3.6 to 9.0, 0.03 to 8.0, and 0.06 to 0.1 mg kg^-1 (dry wt.) respectively. In the oyster, the Cd concentration was well above the safe limit whereas the Pb and Hg concentrations were below the safe limit recommended by the European Commission (EC No. 1881/2006) for human consumption. The MPN value in the raw oyster for fecal coliforms (33-110 × 10³/100 g) exceeded the United States Food and Drug Administration (USFDA) approved limits. Increase in antioxidant enzymes (catalase, superoxide dismutase, glutathione-s-transferase, and metallothionein) activities with increasing pollutants loading was observed. The activities of antioxidant enzymes in the oyster were found to be very useful tool for evaluating environmental condition in any tropical estuarine systems.

A role for Vibrio vulnificus PecS during hypoxia

The genus Vibrio includes serious human pathogens, and mollusks are a significant reservoir for species such as V. vulnificus. Vibrio species encode PecS, a member of the multiple antibiotic resistance regulator (MarR) family of transcription factors; pecS is divergently oriented to pecM, which encodes an efflux pump. We report here that Vibrio species feature frequent duplications of pecS-pecM genes, suggesting evolutionary pressures to respond to distinct environmental situations. The single V. vulnificus PecS binds two sites within the pecS-pecM intergenic region with K_d = 0.3 ± 0.1 nM, a binding that is attenuated by the ligands xanthine and urate, except when promoter DNA is saturated with PecS. A unique target is found in the intergenic region between genes encoding the nitric oxide sensing transcription factor, NsrR, and nod; the nod-encoded nitric oxide dioxygenase is important for preventing nitric oxide stress. Reporter gene assays show that PecS-mediated repression of gene expression can be relieved in presence of ligand. Since xanthine and urate are produced as part of the oxidative burst during host defenses and under molluscan hypoxia, we propose that these intermediates in the host purine degradation pathway function to promote bacterial survival during hypoxia and oxidative stress.

Bacteriophage Interactions with Marine Pathogenic Vibrios: Implications for Phage Therapy

A global distribution in marine, brackish, and freshwater ecosystems, in combination with high abundances and biomass, make vibrios key players in aquatic environments, as well as important pathogens for humans and marine animals. Incidents of Vibrio-associated diseases (vibriosis) in marine aquaculture are being increasingly reported on a global scale, due to the fast growth of the industry over the past few decades years. The administration of antibiotics has been the most commonly applied therapy used to control vibriosis outbreaks, giving rise to concerns about development and spreading of antibiotic-resistant bacteria in the environment. Hence, the idea of using lytic bacteriophages as therapeutic agents against bacterial diseases has been revived during the last years. Bacteriophage therapy constitutes a promising alternative not only for treatment, but also for prevention of vibriosis in aquaculture. However, several scientific and technological challenges still need further investigation before reliable, reproducible treatments with commercial potential are available for the aquaculture industry. The potential and the challenges of phage-based alternatives to antibiotic treatment of vibriosis are addressed in this review.

Detection of Total and Pathogenic Vibrio parahaemolyticus in Shellfish Growing along the South Yellow Sea and the East China Sea

This study was conducted to monitor the densities of total and pathogenic Vibrio parahaemolyticus in 300 samples of nine shellfish species harvested from the coasts of the South Yellow Sea and the East China Sea (N 23° to 34°, E 116° to 124°), People's Republic of China, between May and October 2015. Total V. parahaemolyticus densities were measured, and V. parahaemolyticus isolates were biochemically identified with probes for the thermostable direct hemolysin gene (tdh) and the thermostable direct hemolysin-related hemolysin gene (trh). We found that 202 of the 300 samples were positive for V. parahaemolyticus from all the sites: 58 of the 100 samples from the Fujian province, 71 of the 100 samples from the Zhejiang province, and 73 of the 100 samples from the Jiangsu province. In most (170) of the 300 samples, V. parahaemolyticus densities were 0.3 to 10 most probable number (MPN)/g; five lots exceeded 110 MPN/g, and two lots were estimated at 110 MPN/g. Among the 202 V. parahaemolyticus strains, only one was trh positive. Densities of V. parahaemolyticus in these shellfish were temperature dependent, with highest densities in June and July. Among the nine mollusk species, V. parahaemolyticus was most abundant in the agemaki clam (Sinonovacula constricta). The highest and lowest V. parahaemolyticus prevalences were found in oriental cyclina (Cyclina sinensis, 93.8%) and mussels (Mytilus edulis, 28.1%), respectively. Overall, although V. parahaemolyticus is widely distributed in marine environments, the density of V. parahaemolyticus was low and the prevalence of the main virulence factor was very low in shellfish along the coasts of the South Yellow Sea and East China Sea, which is important from a public health perspective. Data presented here will be useful for correlational research and can be utilized for developing risk management plans that establish food safety guidelines for V. parahaemolyticus in Chinese shellfish.

The ability of algal organic matter and surface runoff to promote the abundance of pathogenic and non-pathogenic strains of Vibrio parahaemolyticus in Long Island Sound, USA

Food safety is a major concern in the shellfish industry, as severe illness can result from consuming shellfish that have accumulated waterborne pathogens. Shellfish harvesting areas are typically monitored for indicator bacteria such as fecal coliforms that serve as proxies for enteric pathogens although these indicators have shown little relation to some naturally occurring pathogenic bacteria such as Vibrio parahaemolyticus. To examine the dynamics and ecology of pathogenic and non-pathogenic strains of V. parahaemolyticus and address the relevance of indicator bacteria in predicting V. parahaemolyticus concentrations, field surveys and experiments were carried out in western Long Island Sound, NY, USA, a region that has experienced recent outbreaks of shellfish contaminated with V. parahaemolyticus. Pathogenic and non-pathogenic strains were quantified via PCR detection of marker genes and most probable number techniques. Field survey data showed little correspondence between fecal coliforms and V. parahaemolyticus, but significant correlations between V. parahaemolyticus and an alternative indicator, enterococci, and between V. parahaemolyticus and short-term (48 h) rainfall were observed. Experiments demonstrated that enrichment of seawater with phytoplankton-derived dissolved organic matter significantly increased the concentration of total V. parahaemolyticus and the presence pathogenic V. parahaemolyticus, but higher temperatures did not. Collectively, these study results suggest that fecal coliforms may fail to account for the full suite of important shellfish pathogens but that enterococci could provide a potential alternative or supplement to shellfish sanitation monitoring. Given the ability of algal-derived dissolved organic matter to promote the growth of pathogenic V. parahaemolyticus, restricting nutrient inputs into coastal water bodies that promote algal blooms may indirectly decrease the proliferation of V. parahaemolyticus and protect public health.

Surface hypothermia predicts murine mortality in the intragastric Vibrio vulnificus infection model

BACKGROUND

The Gram-negative bacterium Vibrio vulnificus can cause severe disease in humans who consume undercooked, contaminated seafood. To study food-borne V. vulnificus disease in the laboratory, mouse virulence studies predominantly use death as the primary experimental endpoint because behaviorally based moribund status does not consistently predict lethality. This study assessed ventral surface temperature (VST) and its association with mouse survival during V. vulnificus virulence studies as an efficacious, humane alternative.

METHODS

VST of mice intragastrically inoculated with V. vulnificus was measured every 2-h for 24 h and data for minimal VST analyzed for prediction of lethal outcome.

RESULTS

In contrast to the relatively stable VST of mock-infected control animals, mice infected with V. vulnificus exhibited hypothermia with minima occurring 8 to 12 h post-inoculation. The minimum VST of mice that proceeded to death was significantly lower than that of surviving mice. VST ≤ 23.5 °C was predictive of subsequent death with a sensitivity of 68% and specificity of 95%.

CONCLUSIONS

Use of VST ≤ 23.5 °C as an experimental endpoint during V. vulnificus infection has potential to reduce suffering of nearly 70% of mice for a mean of 10 h per mouse, without compromising experimental efficacy. Temperature cutoff of 23.5 °C exhibited 93% positive and 77% negative predictive value. For future V. vulnificus virulence studies requiring only binary comparison (e.g., LD50 assays), we find that VST can be applied as a humane endpoint. However, use of VST is not recommended when detailed survival kinetics are desired.

Microbial Diseases of Bivalve Mollusks: Infections, Immunology and Antimicrobial Defense

A variety of bivalve mollusks (phylum Mollusca, class Bivalvia) constitute a prominent commodity in fisheries and aquacultures, but are also crucial in order to preserve our ecosystem’s complexity and function. Bivalve mollusks, such as clams, mussels, oysters and scallops, are relevant bred species, and their global farming maintains a high incremental annual growth rate, representing a considerable proportion of the overall fishery activities. Bivalve mollusks are filter feeders; therefore by filtering a great quantity of water, they may bioaccumulate in their tissues a high number of microorganisms that can be considered infectious for humans and higher vertebrates. Moreover, since some pathogens are also able to infect bivalve mollusks, they are a threat for the entire mollusk farming industry. In consideration of the leading role in aquaculture and the growing financial importance of bivalve farming, much interest has been recently devoted to investigate the pathogenesis of infectious diseases of these mollusks in order to be prepared for public health emergencies and to avoid dreadful income losses. Several bacterial and viral pathogens will be described herein. Despite the minor complexity of the organization of the immune system of bivalves, compared to mammalian immune systems, a precise description of the different mechanisms that induce its activation and functioning is still missing. In the present review, a substantial consideration will be devoted in outlining the immune responses of bivalves and their repertoire of immune cells. Finally, we will focus on the description of antimicrobial peptides that have been identified and characterized in bivalve mollusks. Their structural and antimicrobial features are also of great interest for the biotechnology sector as antimicrobial templates to combat the increasing antibiotic-resistance of different pathogenic bacteria that plague the human population all over the world.

Responses of Mytilus galloprovincialis hemocytes to environmental strains of Vibrio parahaemolyticus, Vibrio alginolyticus, Vibrio vulnificus

Marine bivalves are exposed to different types of bacteria in the surrounding waters, in particular of the Vibrio genus. In the hemocytes of the mussel Mytilus spp. immune responses to different vibrios have been largely characterized. However, little information is available on the hemocyte responses to human pathogenic vibrios commonly detected in coastal waters and bivalve tissues that are involved in seafood-borne diseases. In this work, functional parameters of the hemocytes from the Mediterranean mussel M. galloprovincialis were evaluated in response to in vitro challenge with different vibrios isolated from environmental samples of the Adriatic sea (Italy): V. parahaemolyticus Conero, V. alginolyticus 1513 and V. vulnificus 509. V. parahaemolyticus ATCC 43996 was used for comparison. At the 50:1 bacteria hemocyte ratio, only V. parahaemolyticus strains induced significant lysosomal membrane destabilisation. Stimulation of extracellular lysozyme release, total ROS, O₂^- and NO production were observed, although to different extents and with distinct time courses for different vibrios, V. vulnificus 509 in particular. Further comparisons between V. parahaemolyticus Conero and V. vulnificus 509 showed that only the latter induced dysregulation of the phosphorylation state of p38 MAP Kinase and apoptotic processes. The results indicate that mussel hemocytes can mount an efficient immune response towards V. parahaemolyticus and V. alginolyticus strains, whereas V. vulnificus 509 may affect the hemocyte function. This is the first report on immune responses of mussels to local environmental isolates of human pathogenic vibrios. These data reinforce the hypothesis that Mytilus hemocytes show specific responses to different vibrio species and strains.

Differences in Abundances of Total Vibrio spp., V. vulnificus, and V. parahaemolyticus in Clams and Oysters in North Carolina

Filter feeding shellfish can concentrate pathogenic bacteria, including Vibrio vulnificus and Vibrio parahaemolyticus, as much as 100-fold from the overlying water. These shellfish, especially clams and oysters, are often consumed raw, providing a route of entry for concentrated doses of pathogenic bacteria into the human body. The numbers of foodborne infections with these microbes are increasing, and a better understanding of the conditions that might trigger elevated concentrations of these bacteria in seafood is needed. In addition, if bacterial concentrations in water are correlated with those in shellfish, then sampling regimens could be simplified, as water samples can be more rapidly and easily obtained. After sampling of oysters and clams, either simultaneously or separately, for over 2 years, it was concluded that while Vibrio concentrations in oysters and water were related, this was not the case for levels in clams and water. When clams and oysters were collected simultaneously from the same site, the clams were found to have lower Vibrio levels than the oysters. Furthermore, the environmental parameters that were correlated with levels of Vibrio spp. in oysters and water were found to be quite different from those that were correlated with levels of Vibrio spp. in clams.

IMPORTANCE

This study shows that clams are a potential source of infection in North Carolina, especially for V. parahaemolyticus These findings also highlight the need for clam-specific environmental research to develop accurate Vibrio abundance models and to broaden the ecological understanding of clam-Vibrio interactions. This is especially relevant as foodborne Vibrio infections from clams are being reported.

The Effector Domain Region of the Vibrio vulnificus MARTX Toxin Confers Biphasic Epithelial Barrier Disruption and Is Essential for Systemic Spread from the Intestine

Vibrio vulnificus causes highly lethal bacterial infections in which the Multifunctional Autoprocessing Repeats-in-Toxins (MARTX) toxin product of the rtxA1 gene is a key virulence factor. MARTX toxins are secreted proteins up to 5208 amino acids in size. Conserved MARTX N- and C-terminal repeat regions work in concert to form pores in eukaryotic cell membranes, through which the toxin's central region of modular effector domains is translocated. Upon inositol hexakisphosphate-induced activation of the of the MARTX cysteine protease domain (CPD) in the eukaryotic cytosol, effector domains are released from the holotoxin by autoproteolytic activity. We previously reported that the native MARTX toxin effector domain repertoire is dispensable for epithelial cellular necrosis in vitro, but essential for cell rounding and apoptosis prior to necrotic cell death. Here we use an intragastric mouse model to demonstrate that the effector domain region is required for bacterial virulence during intragastric infection. The MARTX effector domain region is essential for bacterial dissemination from the intestine, but dissemination occurs in the absence of overt intestinal tissue pathology. We employ an in vitro model of V. vulnificus interaction with polarized colonic epithelial cells to show that the MARTX effector domain region induces rapid intestinal barrier dysfunction and increased paracellular permeability prior to onset of cell lysis. Together, these results negate the inherent assumption that observations of necrosis in vitro directly predict bacterial virulence, and indicate a paradigm shift in our conceptual understanding of MARTX toxin function during intestinal infection. Results implicate the MARTX effector domain region in mediating early bacterial dissemination from the intestine to distal organs-a key step in V. vulnificus foodborne pathogenesis-even before onset of overt intestinal pathology.

Effects of triclosan on bacterial community composition and Vibrio populations in natural seawater microcosms

Pharmaceuticals and personal care products, including antimicrobials, can be found at trace levels in treated wastewater effluent. Impacts of chemical contaminants on coastal aquatic microbial community structure and pathogen abundance are unknown despite the potential for selection through antimicrobial resistance. In particular, Vibrio, a marine bacterial genus that includes several human pathogens, displays resistance to the ubiquitous antimicrobial compound triclosan. Here we demonstrated through use of natural seawater microcosms that triclosan (at a concentration of ~5 ppm) can induce a significant Vibrio growth response (68-1,700 fold increases) in comparison with no treatment controls for three distinct coastal ecosystems: Looe Key Reef (Florida Keys National Marine Sanctuary), Doctors Arm Canal (Big Pine Key, FL), and Clam Bank Landing (North Inlet Estuary, Georgetown, SC). Additionally, microbial community analysis by 16 S rRNA gene sequencing for Looe Key Reef showed distinct changes in microbial community structure with exposure to 5 ppm triclosan, with increases observed in the relative abundance of Vibrionaceae (17-fold), Pseudoalteromonadaceae (65-fold), Alteromonadaceae (108-fold), Colwelliaceae (430-fold), and Oceanospirillaceae (1,494-fold). While the triclosan doses tested were above concentrations typically observed in coastal surface waters, results identify bacterial families that are potentially resistant to triclosan and/or adapted to use triclosan as a carbon source. The results further suggest the potential for selection of Vibrio in coastal environments, especially sediments, where triclosan may accumulate at high levels.

Managing marine mollusc diseases in the context of regional and international commerce: policy issues and emerging concerns

Marine mollusc production contributes to food and economic security worldwide and provides valuable ecological services, yet diseases threaten these industries and wild populations. Although the infrastructure for mollusc aquaculture health management is well characterized, its foundations are not without flaws. Use of notifiable pathogen lists can leave blind spots with regard to detection of unlisted and emerging pathogens. Increased reliance on molecular tools has come without similar attention to diagnostic validation, raising questions about assay performance, and has been accompanied by a reduced emphasis on microscopic diagnostic expertise that could weaken pathogen detection capabilities. Persistent questions concerning pathogen biology and ecology promote regulatory paralysis that impedes trade and which could weaken biosecurity by driving commerce to surreptitious channels. Solutions that might be pursued to improve shellfish aquaculture health management include the establishment of more broad-based surveillance programmes, wider training and use of general methods like histopathology to ensure alertness to emerging diseases, an increased focus on assay assessment and validation as fundamental to assay development, investment in basic research, and application of risk analyses to improve regulation. A continual sharpening of diagnostic tools and approaches and deepening of scientific knowledge is necessary to manage diseases and promote sustainable molluscan shellfish industries.