Associations of Environmental Conditions and Vibrio parahaemolyticus Genetic Markers in Washington State Pacific Oysters

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.

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 vulnificus and Vibrio parahaemolyticus in Oysters under Low Tidal Range Conditions: Is Seawater Analysis Useful for Risk Assessment?

Human-pathogenic Vibrio bacteria are acquired by oysters through filtering seawater, however, the relationships between levels of these bacteria in measured in oysters and overlying waters are inconsistent across regions. The reasons for these discrepancies are unclear hindering our ability to assess if -or when- seawater samples can be used as a proxy for oysters to assess risk. We investigated whether concentrations of total and human pathogenic Vibrio vulnificus (vvhA and pilF genes) and Vibrio parahaemolyticus (tlh, tdh and trh genes) measured in seawater reflect concentrations of these bacteria in oysters (Crassostrea virginica) cultured within the US lower Chesapeake Bay region. We measured Vibrio spp. concentrations using an MPN-qPCR approach and analyzed the data using structural equation modeling (SEM). We found seawater concentrations of these bacteria to predictably respond to temperature and salinity over chlorophyll a, pheophytin or turbidity. We also inferred from the SEM results that Vibrio concentrations in seawater strongly predict their respective concentrations in oysters. We hypothesize that such seawater-oyster coupling can be observed in regions of low tidal range. Due to the ease of sampling and processing of seawater samples compared to oyster samples, we suggest that under low tidal range conditions, seawater samples can foster increased spatial and temporal coverage and complement data associated with oyster samples.

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.

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.