Factors affecting the uptake and retention of Vibrio vulnificus in oysters

Prevalence and risk factors of seafood-borne Vibrio vulnificus in Asia: a systematic review with meta-analysis and meta-regression

Vibrio vulnificus is a free-living marine bacterium associated with the contamination of fish and shellfish-the most consumed seafood in Asia. Owing to its potentially lethal clinical consequences, the consumption of seafood contaminated with V. vulnificus has become a growing public health concern. This systematic review with meta-analysis and meta-regression aimed to integrate data on the prevalence of seafood-borne V. vulnificus specifically in Asia and assess the potential risk factors that can influence the outcomes. A comprehensive literature search of four electronic databases yielded 279 relevant studies, among which 38 fulfilled the inclusion criteria. These selected studies were subjected to risk-of-bias assessment and data extraction by three independent researchers. A meta-analysis of the eligible studies estimated the overall prevalence of seafood-borne V. vulnificus in Asia to be 10.47% [95% confidence interval (CI): 6.8-15.8%], with bivalve shellfish, such as oysters, mussels, clams, and cockles being the most contaminated seafood. The highest prevalence was reported in Japan, where 47.6% of the seafood samples tested positive for V. vulnificus. The subgroup and meta-regression analyses identified three potential covariates-detection method, publication year, and country-associated with between-study heterogeneity. Furthermore, data visualization displayed the variations in V. vulnificus prevalence across the studies, associated with differences in sample type, sample size, and sampling stage. This study provides valuable insights into the prevalence of V. vulnificus in fish and shellfish across the entire Asian continent and highlights the potential factors that cause variation in the prevalence rates among the studies. These findings underscore the importance of enhancing hygiene measures throughout the seafood supply chain to mitigate V. vulnificus infection risks and ensure the safety of consumers.

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.

A Novel RAA Combined Test Strip Method Based on Dual Gene Targets for Pathogenic Vibrio vulnificus in Aquatic Products

Vibrio vulnificus can cause disease in aquatic animals and humans, therefore, rapid and simple field detection of pathogenic V. vulnificus is important for early disease prevention. In this study, a novel recombinase-aided amplification (RAA) combined test strip with double T-lines (RAA-TS-DTL) was developed for the rapid detection of V. vulnificus in aquatic products. Pathogenic V. vulnificus was detected using the virulence vvhA gene and the housekeeping gene gyrB gene as the dual target of the test strip. The RAA-TS-DTL method showed 100% specificity for V. vulnificus, and no cross-reaction was observed with Vibrio spp. or other bacteria (n = 14). Furthermore, sensitive detection of V. vulnificus in oysters was achieved. The LODs of the gyrB and vvhA genes were 6 CFU/mL and 23 CFU/mL, respectively, which was about five times higher than that of the commercial test strip. The method was validated with spiked samples (n = 60) of fish, shrimp and oyster. The consistency between RAA-TS-DTL and the traditional culture method was 97.9%. In addition, the entire process of detection, including preparation of the sample, could be completed within 50 min. Our results indicated that the developed RAA-TS-DTL was a reliable and useful tool for rapid screening or on-site detection of pathogenic V. vulnificus in aquatic products and aquaculture water.

Fulminant Overwhelming Necrotizing Vibrio vulnificus Sepsis Secondary to Oyster Consumption

Vibrio vulnificus is an opportunistic gram-negative rod-shaped bacteria found in warm, low salinity waters. Transmission through open wounds or consumption of contaminated seafood can lead to wound infections, sepsis, and potentially death. A 44-year-old man with a history of poly-substance abuse, cirrhosis, and recent oyster consumption presented to the emergency department in June with acute onset bilateral leg pain associated with rash and fever. Within 6 hours of his arrival, the rash rapidly progressed to large bullae with extensive necrosis ascending to the level of the abdomen, and he developed septic shock. Despite prompt surgical intervention and appropriate antibiotic and resuscitative therapies, the patient had progressive multi-system organ failure and died 7 days after admission. Concurrent necrotizing fasciitis with sepsis secondary to V. vulnificus infection is rare and potentially fatal, as demonstrated in this case.

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.

The Viable but Non-Culturable (VBNC) State in Vibrio Species: Why Studying the VBNC State Now Is More Exciting than Ever

During periods that are not conducive for growth or when facing stressful conditions, Vibrios enter a dormant state called the Viable But Non-Culturable (VBNC) state. In this chapter, I will analyse the role of the VBNC state in Vibrio species survival and pathogenesis and the molecular mechanisms regulating this complex phenomenon. I will emphasise some of the novel findings that make studying the VBNC state now more exciting than ever and its significance in the epidemiology of these pathogens and critical role in food safety.

Life history of oysters influences Vibrio parahaemolyticus accumulation in Pacific oysters (Crassostrea gigas)

Vibrio parahaemolyticus infection in humans is associated with raw oyster consumption. Evaluation of V. parahaemolyticus presence in oysters is of most interest because of the economic and public health issues that it represents. To explore V. parahaemolyticus accumulation and depuration in adult Crassostrea gigas, we developed a GFP-tagged V. parahaemolyticus strain (IFVp201-gfp⁺ ), as well as a rapid and efficient quantification method in C. gigas oysters haemolymph by flow cytometry. Impact of the life history of C. gigas on accumulation and depuration of V. parahaemolyticus IFVp201 was subsequently investigated. We found that naive oysters, i.e. grown in controlled facilities with UV treated seawater, accumulated significantly more IFVp201 than environmental oysters, i.e. grown in intertidal environment. We hypothesized that environmental oysters could have been immune primed, thus could limit V. parahaemolyticus accumulation. Meanwhile, both naive and environmental oysters had similar depuration rates.

Effects of curcumin-mediated photodynamic treatment on lipid degradation of oysters during refrigerated storage

BACKGROUND

Oyster's lipid degradation leads to a decrease in edible and nutritional value. Curcumin-mediated photodynamic treatment (PDT) is an innovative non-thermal technology, although evaluation of the oyster's lipid degradation has been scarce. In the present study, we investigated peroxide value, thiobarbituric acid reactive substance, triacylglycerol and free fatty acids to evaluate the effect of curcumin-mediated PDT on lipid degradation of oysters during refrigerated storage.

RESULTS

The results showed that curcumin-mediated PDT could delay oyster's lipid degradation. Next, the activities of enzymes were detected to determine the mechanisms behind the effects of curcumin-mediated PDT. It was revealed that the activities of lipase, phospholipase A₂ (PLA₂ ), phospholipase C (PLC), phospholipase D (PLD) and lipoxygenase (LOX) were significantly inhibited after curcumin-mediated PDT (P < 0.05). Furthermore, 16 s rRNA analysis established that the relative abundances of Pseudoalteromonas and Psychrilyobacter were reduced by 51.58% and 43.82%, respectively, after curcumin-mediated PDT.

CONCLUSION

Curcumin-mediated PDT could delay oyster's lipid degradation by inhibiting the activities of lipase, PLA₂ , PLC, PLD and LOX, as well as by changing the oyster's microbial composition, reducing the relative abundance of Pseudoalteromonas and Psychrilyobacter. © 2021 Society of Chemical Industry.

In situ dynamics of Vibrio parahaemolyticus and Vibrio vulnificus in water, sediment and triploid Crassostrea virginica oysters cultivated in floating gear

AIMS

To understand spatial-temporal distribution of V. parahaemolyticus and V. vulnificus in triploid C. virginica in off-bottom aquaculture.

METHODS AND RESULTS

Oysters, sediments, and water were seasonally collected in Georgia, USA. V. parahaemolyticus and V. vulnificus were quantified with tlh/tdh/trh, and vvhA genes, respectively. No tdh/trh genes were detected. Highest concentrations of tlh gene were observed in summer sediments > oysters > water (10⁵ /g, 10⁴ /g, 10³ /ml). VvhA concentrations were similar in sediments and oysters but never exceeded ≥ 3x10¹ /ml in water. Concentrations of tlh and vvhA genes correlated to temperature and turbidity, respectively; which along with their different spatial distribution indicated different environmental drivers. In oysters, ratios of the tlh and vvhA to 16S rRNA gene have increased from 0 to 10^-1 and 10^-2 in summer, while these ratios in water and sediments were lower by 2-3 orders of magnitude.

CONCLUSIONS

Dynamics of tlh and vvhA concentrations and abundances suggested enrichment of V. parahaemolyticus and V. vulnificus by off-bottom triploid oysters in summer resulting in their abundance by far exceeding that in water.

SIGNIFICANCE AND IMPACT OF THE STUDY

This first report on enrichment of Vibrio pathogens in triploid oysters with no direct contact to sediments reveals a threat to human health suggesting their monitoring in triploid off-bottom C. virginica aquaculture.

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.

Bacterial dormancy: A subpopulation of viable but non-culturable cells demonstrates better fitness for revival

The viable but non culturable (VBNC) state is a condition in which bacterial cells are viable and metabolically active, but resistant to cultivation using a routine growth medium. We investigated the ability of V. parahaemolyticus to form VBNC cells, and to subsequently become resuscitated. The ability to control VBNC cell formation in the laboratory allowed us to selectively isolate VBNC cells using fluorescence activated cell sorting, and to differentiate subpopulations based on their metabolic activity, cell shape and the ability to cause disease in Galleria mellonella. Our results showed that two subpopulations (P1 and P2) of V. parahaemolyticus VBNC cells exist and can remain dormant in the VBNC state for long periods. VBNC subpopulation P2, had a better fitness for survival under stressful conditions and showed 100% revival under favourable conditions. Proteomic analysis of these subpopulations (at two different time points: 12 days (T12) and 50 days (T50) post VBNC) revealed that the proteome of P2 was more similar to that of the starting microcosm culture (T0) than the proteome of P1. Proteins that were significantly up or down-regulated between the different VBNC populations were identified and differentially regulated proteins were assigned into 23 functional groups, the majority being assigned to metabolism functional categories. A lactate dehydrogenase (lldD) protein, responsible for converting lactate to pyruvate, was significantly upregulated in all subpopulations of VBNC cells. Deletion of the lactate dehydrogenase (RIMD2210633:ΔlldD) gene caused cells to enter the VBNC state significantly more quickly compared to the wild-type, and adding lactate to VBNC cells aided their resuscitation and extended the resuscitation window. Addition of pyruvate to the RIMD2210633:ΔlldD strain restored the wild-type VBNC formation profile. This study suggests that lactate dehydrogenase may play a role in regulating the VBNC state.

Oyster Calcifying Fluid Harbors Persistent and Dynamic Autochthonous Bacterial Populations That May Aid in Shell Formation

The eastern oyster (Crassostrea virginica) is a keystone species in estuarine environments but faces threats to shell formation associated with warming temperatures and acidification. Extrapallial fluid (EF), which is responsible for shell formation, harbors diverse and abundant microbial communities. Commensal microbial communities are vital to host health and fitness, yet long-term studies investigating temporal responses of the EF microbiome and its function in oyster fitness are lacking. In this study, bacterial communities of oyster EF and the water column were characterized monthly from October 2010 to September 2011. We investigated the selection, composition, and dynamics of resident and transient community members, evaluated the impact of temperature on EF microbial communities, and examined the functional role of the EF microbiome. Oyster EF communities were significantly different from the water column and were enriched for several taxa, including the Deltaproteobacteria, Epsilonproteobacteria, and Gammaproteobacteria. Overall, 94 resident members were identified in oyster EF. These members were persistent and abundant, comprising on average 33% of EF communities. Resident EF communities formed high-temperature and low-temperature groups and were more abundant overall at colder temperatures. Oyster EF resident communities were predicted to be enriched for dissimilatory nitrate reduction, nitrogen fixation, nitrification, and sulfite reductase genes. Sulfate and nitrate reduction may have a synergistic effect on calcium carbonate precipitation and indirectly aid in shell formation. Therefore, the potential role of the oyster EF microbiome in shell formation warrants further investigation as oysters and other shellfish face the future impacts of ocean warming and acidification.

Spatial Heterogeneity of Vibrio spp. in Sediments of Chinese Marginal Seas

Vibrio spp. are ubiquitous marine bacteria with high metabolism flexibility and genome plasticity. Previous studies have revealed the dynamics of planktonic vibrios in relation to environmental forces, such as temperature and salinity. However, little is known about Vibrio ecology in benthic environments. Here, we elucidate the abundance, diversity, and spatial distribution of Vibrio spp. in sediments of the Chinese marginal seas, with a wide spatial range from north to south covering the Yellow Sea (YS), East China Sea (ECS), and South China Sea (SCS). Quantitative analysis showed that Vibrio spp. were most abundant in the SCS (∼9.04 × 10⁵ copies/g) compared to the YS (∼1.00 × 10⁵ copies/g) and ECS (∼8.86 × 10⁵ copies/g). Vibrio community compositions derived from Illumina sequencing of Vibrio-specific 16S rRNA genes varied significantly between sampling areas, which was reflected by a strong distance-decay pattern. The spatial distribution of Vibrio was governed by a joint effect of spatial and environmental factors (especially temperature, salinity, and SiO₃ ^2-), and their respective pure effects explained only a small fraction of the community variation. Moreover, we identified the most prominent operational taxonomic units (OTUs) that were partitioned in these sea areas. Whereas Vibrionaceae OTU20 and Photobacterium lipolyticum were prevalent in the YS, Vibrio gigantis and Photobacterium piscicola, and P. piscicola, Photobacterium lutimaris, and Photobacterium alginatilyticum were prevalent in the ECS and SCS, respectively. Our study demonstrated clear spatial heterogeneity of Vibrio spp. in sediments of the Chinese marginal seas, laying a foundation for fully understanding the marine Vibrio ecology and the ecological roles of the species.IMPORTANCE Vibrio is an important component of natural marine microbial populations in terms of pathogenicity and roles in carbon cycling. Compared to the marine pelagic environment, our knowledge of the diversity and distribution pattern of Vibrio spp. in sediment is limited. Here, we show higher Vibrio abundance in Chinese marginal seas than in other studied sediments. There was a clear spatial differentiation of Vibrio abundance and community composition in different sea areas. The benthic Vibrio community displayed a strong distance-decay pattern across a wide spatial range, which was formed under the combined effects of spatial and environmental factors. These results provide deep insights into the ecological dynamics of Vibrio and its environmental controls, facilitating a more comprehensive understanding of the marine Vibrio ecology.

Long-Term Depuration of Crassostrea virginica Oysters at Different Salinities and Temperatures Changes Vibrio vulnificus Counts and Microbiological Profile

Previous short-duration depuration studies with the eastern oyster ( Crassostrea virginica) demonstrated difficulty in achieving significant naturally incurred Vibrio vulnificus population count reductions. The present study used long-duration depuration (14 days) at controlled temperatures (10 or 22°C) and salinities (12, 16, or 20 mg/g). All depuration temperature-salinity combinations significantly reduced V. vulnificus counts, with greatest reductions seen in 12 mg/g, 10°C seawater (2.7-log CFU/g reduction) and in 20 mg/g, 22°C seawater (2.8-log reduction). Mesophilic vibrios dominated the overall microflora of freshly harvested oysters, whereas refrigerated storage selected for psychrotrophic bacteria ( Pseudomonas spp., Aeromonas spp., Shewanella spp., Psychrobacter spp.) as well as did depuration at 10°C ( Pseudoalteromonas spp., Shewanella spp., Vibrio spp.). Depuration at 22°C retained dominance of mesophilic vibrios, including pathogenic species, followed by Shewanella spp., Pseudoalteromonas spp., and Photobacterium spp. Although aerobic plate counts were lower in 22°C depurated oysters (5.0 log versus 6.0 log) compared with 10°C, depuration at 10°C offered greater V. vulnificus population reductions than depuration at 22°C. This advantage was only seen at 12 mg/g salinity, with no impact at 16 and 20 mg/g salinities. No depuration treatment reduced V. vulnificus counts to nondetectable levels. Use of prolonged depuration may be a helpful intervention to control V. vulnificus populations in oysters.

Uncovering the geographical and host impacts on the classification of Vibrio vulnificus

Vibrio vulnificus causes human sickness throughout the world via the consumption of undercooked seafood or exposure to contaminated water. Previous attempts at phylogenetic analyses of V. vulnificus have proven unsuccessful, mainly due to the poorly understood impact of factors on its divergence. In this study, we used advanced statistical and phylogenetic methods to strengthen the classification of V. vulnificus. This updated classification included the impact of geographical and host factors. The results demonstrate the existence of hierarchies and multidimensional effects in the classification of V. vulnificus, from the molecular level using biotypes, to the distributional level using geographical location, to the adaptational level through host immune response. These findings have implications for the classification of bacteria, bacterial evolution, and public health.

Vibrio Ecology in the Neuse River Estuary, North Carolina, Characterized by Next-Generation Amplicon Sequencing of the Gene Encoding Heat Shock Protein 60 (hsp60)

Of marine eubacteria, the genus Vibrio is intriguing because member species are relevant to both marine ecology and human health. Many studies have touted the relationships of Vibrio to environmental factors, especially temperature and salinity, to predict total Vibrio abundance but lacked the taxonomic resolution to identify the relationships among species and the key drivers of Vibrio dynamics. To improve next-generation sequencing (NGS) surveys of Vibrio, we have conducted both 16S small subunit rRNA and heat shock protein 60 (hsp60) amplicon sequencing of water samples collected at two well-studied locations in the Neuse River Estuary, NC. Samples were collected between May and December 2016 with enhanced sampling efforts in response to two named storms. Using hsp60 sequences, 21 Vibrio species were identified, including the potential human pathogens V. cholerae, V. parahaemolyticus, and V. vulnificus Changes in the Vibrio community mirrored seasonal and storm-related changes in the water column, especially in response to an influx of nutrient-rich freshwater to the estuary after Hurricane Matthew, which initiated dramatic changes in the overall Vibrio community. Individual species dynamics were wide ranging, indicating that individual Vibrio taxa have unique ecologies and that total Vibrio abundance predictors are insufficient for risk assessments of potentially pathogenic species. Positive relationships between Vibrio, dinoflagellates, and Cyanobacteria were identified, as were intraspecies associations, which further illuminated the interactions of cooccurring Vibrio taxa along environmental gradients.IMPORTANCE The objectives of this research were to utilize a novel approach to improve sequence-based surveys of Vibrio communities and to demonstrate the usefulness of this approach by presenting an analysis of Vibrio dynamics in the context of environmental conditions, with a particular focus on species that cause disease in humans and on storm effects. The methods presented here enabled the analysis of Vibrio dynamics with excellent taxonomic resolution and could be incorporated into future ecological studies and risk prediction strategies for potentially pathogenic species. Next-generation sequencing of hsp60 and other innovative sequence-based approaches are valuable tools and show great promise for studying Vibrio ecology and associated public health risks.

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.

Oysters and Vibrios as a Model for Disease Dynamics in Wild Animals

Disease dynamics in the wild are influenced by a number of ecological and evolutionary factors not addressed by traditional laboratory-based characterization of pathogens. Here we propose the oyster, Crassostrea gigas, as a model for studying the interaction of the environment, bacterial pathogens, and the host in disease dynamics. We show that an important first step is to ask whether the functional unit of pathogenesis is a bacterial clone, a population, or a consortium in order to assess triggers of disease outbreaks and devise appropriate monitoring tools. Moreover, the development of specific-pathogen-free (SPF) oysters has enabled assessment of the infection process under natural conditions. Finally, recent results show the importance of microbial interactions and host genetics in determining oyster health and disease.

Vibrio bacteria in raw oysters: managing risks to human health

The human-pathogenic marine bacteria Vibrio vulnificus and V. parahaemolyticus are strongly correlated with water temperature, with concentrations increasing as waters warm seasonally. Both of these bacteria can be concentrated in filter-feeding shellfish, especially oysters. Because oysters are often consumed raw, this exposes people to large doses of potentially harmful bacteria. Various models are used to predict the abundance of these bacteria in oysters, which guide shellfish harvest policy meant to reduce human health risk. Vibrio abundance and behaviour varies from site to site, suggesting that location-specific studies are needed to establish targeted risk reduction strategies. Moreover, virulence potential, rather than simple abundance, should be also be included in future modeling efforts.