Forecasting Seasonal Vibrio parahaemolyticus Concentrations in New England Shellfish

Tracking Vibrio: population dynamics and ecology of Vibrio parahaemolyticus and V. vulnificus in an Alabama estuary

Vibrio is a genus of halophilic, gram-negative bacteria found in estuaries around the globe. Integral parts of coastal cultures often involve contact with vectors of pathogenic Vibrio spp. (e.g., consuming raw shellfish). High rates of mortality from certain Vibrio spp. infections demonstrate the need for an improved understanding of Vibrio spp. dynamics in estuarine regions. Our study assessed meteorological, hydrographic, and biological correlates of Vibrio parahaemolyticus and V. vulnificus at 10 sites in the Eastern Mississippi Sound System (EMSS) from April to October 2019. During the sampling period, median abundances of V. parahaemolyticus and V. vulnificus were 2.31 log MPN/L and 2.90 log MPN/L, respectively. Vibrio spp. dynamics were largely driven by site-based variation, with sites closest to freshwater inputs having the highest abundances. The E-W wind scalar, which affects Ekman transport, was a novel Vibrio spp. correlate observed. A potential salinity effect on bacterial-particle associations was identified, where V. vulnificus was associated with larger particles in conditions outside of their optimal salinity. Additionally, V. vulnificus abundances were correlated to those of harmful algal species that did not dominate community chlorophyll. Correlates from this study may be used to inform the next iteration of regionally predictive Vibrio models and may lend additional insight to Vibrio spp. ecology in similar systems.

IMPORTANCE

Vibrio spp. are bacteria found in estuaries worldwide; some species can cause illness and infections in humans. Relationships between Vibrio spp. abundance, salinity, and temperature are well documented, but correlations to other environmental parameters are less understood. This study identifies unique correlates (e.g., E-W wind scalar and harmful algal species) that could potentially inform the next iteration of predictive Vibrio models for the EMSS region. Additionally, these correlates may allow existing environmental monitoring efforts to be leveraged in providing data inputs for future Vibrio risk models. An observed correlation between salinity and V. vulnificus/particle-size associations suggests that predicted environmental changes may affect the abundance of Vibrio spp. in certain reservoirs, which may alter which vectors present the greatest vibrio risk.

Inoviridae prophage and bacterial host dynamics during diversification, succession, and Atlantic invasion of Pacific-native Vibrio parahaemolyticus

IMPORTANCE

An understanding of the processes that contribute to the emergence of pathogens from environmental reservoirs is critical as changing climate precipitates pathogen evolution and population expansion. Phylogeographic analysis of Vibrio parahaemolyticus hosts combined with the analysis of their Inoviridae phage resolved ambiguities of diversification dynamics which preceded successful Atlantic invasion by the epidemiologically predominant ST36 lineage. It has been established experimentally that filamentous phage can limit host recombination, but here, we show that phage loss is linked to rapid bacterial host diversification during epidemic spread in natural ecosystems alluding to a potential role for ubiquitous inoviruses in the adaptability of pathogens. This work paves the way for functional analyses to define the contribution of inoviruses in the evolutionary dynamics of environmentally transmitted pathogens.

The impact of global warming on the signature virulence gene, thermolabile hemolysin, of Vibrio parahaemolyticus

IMPORTANCE

In this study, Vibrio parahaemolyticus strains were collected from a large number of aquatic products globally and found that temperature has an impact on the virulence of these bacteria. As global temperatures rise, mutations in a gene marker called thermolabile hemolysin (tlh) also increase. This suggests that environmental isolates adapt to the warming environment and become more pathogenic. The findings can help in developing tools to analyze and monitor these bacteria as well as assess any link between climate change and vibrio-associated diseases, which could be used for forecasting outbreaks associated with them.

Fitness and transcriptomic analysis of pathogenic Vibrio parahaemolyticus in seawater at different shellfish harvesting temperatures

IMPORTANCE

Given the involvement of Vibrio parahaemolyticus (Vp) in a wide range of seafood outbreaks, a systematical characterization of Vp fitness and transcriptomic changes at temperatures of critical importance for seafood production and storage is needed. In this study, one of each virulent Vp strain (tdh+ and trh+) was tested. While no difference in survival behavior of the two virulent strains was observed at 10°C, the tdh+ strain had a faster growth rate than the trh+ strain at 30°C. Transcriptomic analysis showed that a significantly higher number of genes were upregulated at 30°C than at 10°C. The majority of differentially expressed genes of Vp at 30°C were annotated to functional categories supporting cellular growth. At 10°C, the downregulation of the biofilm formation and histidine metabolism indicates that the current practice of storing seafood at low temperatures not only protects seafood quality but also ensures seafood safety.

Optimum environmental conditions controlling prevalence of vibrio parahaemolyticus in marine environment

This literature review presents major environmental indicators and their optimum variation ranges for the prevalence of Vibrio parahaemolyticus in the marine environment by critically reviewing and statistically analyzing more than one hundred studies from countries around the world. Results of this review indicated that the prevalence of Vibrio parahaemolyticus in the marine environment is primarily responsive to favorable environmental conditions that are described with environmental indicators. The importance of environmental indicators to the prevalence of Vibrio parahaemolyticus can be ranked from the highest to lowest as Sea Surface Temperature (SST), salinity, pH, chlorophyll a, and turbidity, respectively. It was also found in this study that each environmental indicator has an optimum variation range favoring the prevalence of Vibrio parahaemolyticus. Specifically, the SST range of 25.67 ± 2 °C, salinity range of 27.87 ± 3 ppt, and pH range of 7.96 ± 0.1 were found to be the optimum conditions for the prevalence of Vibrio parahaemolyticus. High vibrio concentrations were also observed in water samples with the chlorophyll a range of 16-25 μg/L. The findings provide new insights into the importance of environmental indicators and their optimum ranges, explaining not only the existence of both positive and negative associations reported in the literature but also the dynamic associations between the Vibrio presence and its environmental drivers.

Investigating the Relationship between Nitrate, Total Dissolved Nitrogen, and Phosphate with Abundance of Pathogenic Vibrios and Harmful Algal Blooms in Rehoboth Bay, Delaware

Vibrio-associated illnesses have been expanding globally over the past several decades (A. Newton, M.

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.

Transcriptome analysis of Neocaridina denticulate sinensis challenged by Vibrio parahemolyticus

As a common aquatic pathogen, Vibrio parahaemolyticus can cause a variety of diseases of shrimp, especially acute hepatopancreatic necrosis disease (AHPND), which leads to great losses to the aquaculture industry around the world. However, the molecular mechanism of V. parahaemolyticus infection is still unclear. Neocaridina denticulate sinensis is a kind of small ornamental shrimp that is popular in aquarium trade, and due to its tenacious vitality, rapid growth, high reproductive capacity, it is very suitable to be developed as an animal model for basic research on decapod crustaceans. Thus, in this paper, transcriptomes of N. denticulate sinensis hepatopancreas with or without V. parahaemolyticus injection were explored. The results showed that a total of 23,624 genes with the N50 of 2705 bp were obtained. Comparative transcriptomic analysis revealed 21,464 differentially expressed genes between the V. parahaemolyticus infected and non-infected group, of which, 11,127 genes were up-regulated and 10,337 genes were down-regulated. Functional enrichment analysis suggested that many DEGs enriched in immune related pathways, including MAPK signaling pathway, Phosphatidylinositol signaling system, Chemokine signaling pathway, Phagosome and Jak-STAT signaling pathway and so on. Eight genes were selected randomly for qRT-PCR to verify the transcriptome sequencing results and the results showed the expression of these genes were consistent with the transcriptome results. Our work provides a unique and important dataset that contributes to the understanding of the molecular mechanisms of the immune response to V. parahaemolyticus infection and may further provide the basis for the prevention and resolution of bacterial diseases.

The Seasonal Microbial Ecology of Plankton and Plankton-Associated Vibrio parahaemolyticus in the Northeast United States

Microbial ecology studies have proven to be important resources for improving infectious disease response and outbreak prevention. Vibrio parahaemolyticus is an ongoing source of shellfish-borne food illness in the Northeast United States, and there is keen interest in understanding the environmental conditions that coincide with V. parahaemolyticus disease risk, in order to aid harvest management and prevent further illness. Zooplankton and chitinous phytoplankton are associated with V. parahaemolyticus dynamics elsewhere; however, this relationship is undetermined for the Great Bay estuary (GBE), an important emerging shellfish growing region in the Northeast United States. A comprehensive evaluation of the microbial ecology of V. parahaemolyticus associated with plankton was conducted in the GBE using 3 years of data regarding plankton community, nutrient concentration, water quality, and V. parahaemolyticus concentration in plankton. The concentrations of V. parahaemolyticus associated with plankton were highly seasonal, and the highest concentrations of V. parahaemolyticus cultured from zooplankton occurred approximately 1 month before the highest concentrations of V. parahaemolyticus from phytoplankton. The two V. parahaemolyticus peaks corresponded with different water quality variables and a few highly seasonal plankton taxa. Importantly, V. parahaemolyticus concentrations and plankton community dynamics were poorly associated with nutrient concentrations and chlorophyll a, commonly applied proxy variables for assessing ecological health risks and human health risks from harmful plankton and V. parahaemolyticus elsewhere. Together, these statistical associations (or lack thereof) provide valuable insights to characterize the plankton-V. parahaemolyticus dynamic and inform approaches for understanding the potential contribution of plankton to human health risks from V. parahaemolyticus for the Northeast United States.

IMPORTANCE The Vibrio-plankton interaction is a focal relationship in Vibrio disease research; however, little is known about this dynamic in the Northeast United States, where V. parahaemolyticus is an established public health issue. We integrated phototactic plankton separation with seasonality analysis to determine the dynamics of the plankton community, water quality, and V. parahaemolyticus concentrations. Distinct bimodal peaks in the seasonal timing of V. parahaemolyticus abundance from phyto- versus zooplankton and differing associations with water quality variables and plankton taxa indicate that monitoring and forecasting approaches should consider the source of exposure when designing predictive methods for V. parahaemolyticus. Helicotheca tamensis has not been previously reported in the GBE. Its detection during this study provides evidence of the changes occurring in the ecology of regional estuaries and potential mechanisms for changes in V. parahaemolyticus populations. The Vibrio monitoring approaches can be translated to aid other areas facing similar public health challenges.

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.

Responses of Free-Living Vibrio Community to Seasonal Environmental Variation in a Subtropical Inland Bay

Vibrio are widely distributed in aquatic environments and strongly associated with eutrophic environments and human health through the consumption of contaminated seafood. However, the response of the Vibrio community to seasonal variation in eutrophic environments is poorly understood. In this study, we used a Vibrio-specific 16S rRNA sequencing approach to reveal the seasonal distribution pattern and diversity of the Vibrio community in the Maowei Sea, Beibu Gulf of China. The Shannon diversity of the Vibrio community was highest in the summer, while β-diversity analysis showed that Vibrio community structures were significantly different between seasons. Distance-based redundancy analysis (dbRDA) and Mantel test analysis suggested that total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), dissolved inorganic nitrogen (DIN), salinity, and temperature were the key environmental factors shaping the Vibrio community structure, indicating a strong filtering effect of trophic condition on Vibrio communities. Furthermore, through random forest analysis, V. fluvialis, V. alginolyticus, V. proteolyticus, V. splendidus, and the other eight Vibrio species were more sensitive to eutrophic changes. This study revealed seasonal changes in Vibrio communities and the influence of environmental variation on Vibrio community composition, contributing to a better understanding of their potential ecological roles in a subtropical inland bay.

Seasonal and Geographical Differences in Total and Pathogenic Vibrio parahaemolyticus and Vibrio vulnificus Levels in Seawater and Oysters from the Delaware and Chesapeake Bays Determined Using Several Methods

Oyster and seawater samples were collected from five sites in the Chesapeake Bay, MD, and three sites in the Delaware Bay, DE, from May to October 2016 and 2017. Abundances and detection frequencies for total and pathogenic Vibrio parahaemolyticus and Vibrio vulnificus were compared using the standard most-probable-number-PCR (MPN-PCR) assay and a direct-plating (DP) method on CHROMagar Vibrio for total (tlh⁺ ) and pathogenic (tdh⁺ and trh⁺ ) V. parahaemolyticus genes and total (vvhA) and pathogenic (vcgC) V. vulnificus genes. The colony overlay procedure for peptidases (COPP) assay was evaluated for total Vibrionaceae DP had high false-negative rates (14 to 77%) for most PCR targets and was deemed unsatisfactory. Logistic regression models of the COPP assay showed high concordances with MPN-PCR for tdh ⁺ and trh ⁺ V. parahaemolyticus and vvhA ⁺ V. vulnificus in oysters (85.7 to 90.9%) and seawater (81.1 to 92.7%) when seawater temperature and salinity were factored into the model, suggesting that the COPP assay could potentially serve as a more rapid method to detect vibrios in oysters and seawater. Differences in total Vibrionaceae and pathogenic Vibrio abundances between state sampling sites over different collection years were contrasted for oysters and seawater by MPN-PCR. Abundances of tdh ⁺ and trh ⁺ V. parahaemolyticus were ∼8-fold higher in Delaware oysters than in Maryland oysters, whereas abundances of vcgC ⁺ V. vulnificus were nearly identical. For Delaware oysters, 93.5% were both tdh ⁺ and trh ⁺, compared to only 19.2% in Maryland. These results indicate that pathogenic V. parahaemolyticus was more prevalent in the Delaware Bay than in the Chesapeake Bay.IMPORTANCE While V. parahaemolyticus and V. vulnificus cause shellfish-associated morbidity and mortality among shellfish consumers, current regulatory assays for vibrios are complex, time-consuming, labor-intensive, and relatively expensive. In this study, the rapid, simple, and inexpensive COPP assay was identified as a possible alternative to MPN-PCR for shellfish monitoring. This paper shows differences in total Vibrionaceae and pathogenic vibrios found in seawater and oysters from the commercially important Delaware and Chesapeake Bays. Vibrio parahaemolyticus isolates from the Delaware Bay were more likely to contain commonly recognized pathogenicity genes than those from the Chesapeake Bay.

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.