Development and Validation of a Predictive Model for the Growth of Vibrio vulnificus in Postharvest Shellstock Oysters

Vibrio parahaemolyticus and Vibrio vulnificus can grow rapidly in shellfish subjected to ambient air conditions, such as during intertidal exposure. In this study, levels of total and pathogenic (tdh ؉ and/or trh ؉ ) V. parahaemolyticus and total V. vulnificus were determined in oysters collected from two study locations where intertidal harvest practices are common. Samples were collected directly off intertidal flats, after exposure (ambient air [Washington State] or refrigerated [New Jersey]), and after reimmersion by natural tidal cycles. Samples were processed using a most-probable-number (MPN) real-time PCR method for total and pathogenic V. parahaemolyticus or V. vulnificus. In Washington State, the mean levels of V. parahaemolyticus increased 1.38 log MPN/g following intertidal exposure and dropped 1.41 log MPN/g after reimmersion for 1 day, but the levels were dependent upon the container type utilized. Pathogenic V. parahaemolyticus levels followed a similar trend. However, V. vulnificus levels increased 0.10 log MPN/g during intertidal exposure in Washington but decreased by >1 log MPN/g after reimmersion. In New Jersey, initial levels of all vibrios studied were not significantly altered during the refrigerated sorting and containerizing process. However, there was an increase in levels after the first day of reimmersion by 0.79, 0.72, 0.92, and 0.71 log MPN/g for total, tdh ؉ and trh ؉ V. parahaemolyticus, and V. vulnificus, respectively. The levels of all targets decreased to those similar to background after a second day of reimmersion. These data indicate that the intertidal harvest and handling practices for oysters that were studied in Washington and New Jersey do not increase the risk of illness from V. parahaemolyticus or V. vulnificus. IMPORTANCEVibrio parahaemolyticus and Vibrio vulnificus are the leading causes of seafood-associated infectious morbidity and mortality in the United States. Vibrio spp. can grow rapidly in shellfish subjected to ambient air conditions, such as during periods of intertidal exposure. When oysters are submersed with the incoming tide, the vibrios can be purged. However, data on the rates of increase and purging during intertidal harvest are scarce, which limits the accuracy of risk assessments. The objective of this study was to help fill these data gaps by determining the levels of total and pathogenic (tdh ؉ and/or trh ؉ ) V. parahaemolyticus and V. vulnificus in oysters from two locations where intertidal harvest practices are common, using the current industry practices. The data generated provide insight into the responses of Vibrio spp. to relevant practices of the industry and public health, which can be incorporated into risk management decisions. V ibrio spp. are the leading cause of seafood-associated infectious illness and mortality in the United States (1). The two species most frequently associated with infection are Vibrio parahaemolyticus and Vibrio vulnificus. V. parahaemolyticus is the most frequent cause of vibriosis, and infection typi...

mentioning

confidence: 99%

Effects of Intertidal Harvest Practices on Levels of Vibrio parahaemolyticus and Vibrio vulnificus Bacteria in Oysters

Jones

Kinsey

Johnson

et al. 2016

“…The inability of oysters to expel these growing bacteria also contributes to their increased numbers. Currently, federal regulations are in place that limit the time oysters can be exposed to warm air temperatures during harvest (23)(24)(25)(26).Salinity is also a factor in Vibrio abundance. V. vulnificus and V. parahaemolyticus concentrations in oysters appear to have a nonlinear relationship with water column salinity, although this is confounded by conflicting reports of positive, negative, and noncorrelating data (3,13,15,16,(27)(28)(29)(30)(31)(32)(33)(34)(35).…”

mentioning

confidence: 99%

mentioning

confidence: 99%

Development of a Matrix Tool for the Prediction of Vibrio Species in Oysters Harvested from North Carolina

Froelich

Ayrapetyan

Fowler

et al. 2015

The United States has federal regulations in place to reduce the risk of seafood-related infection caused by the estuarine bacteria Vibrio vulnificus and Vibrio parahaemolyticus. However, data to support the development of regulations have been generated in a very few specific regions of the nation. More regionally specific data are needed to further understand the dynamics of human infection relating to shellfish-harvesting conditions in other areas. In this study, oysters and water were collected from four oyster harvest sites in North Carolina over an 11-month period. Samples were analyzed for the abundances of total Vibrio spp., V. vulnificus, and V. parahaemolyticus; environmental parameters, including salinity, water temperature, wind velocity, and precipitation, were also measured simultaneously. By utilizing these data, preliminary predictive management tools for estimating the abundance of V. vulnificus bacteria in shellfish were developed. This work highlights the need for further research to elucidate the full suite of factors that drive V. parahaemolyticus abundance. In the United States, it is estimated that as many as 84,000 people annually contract food-borne infections caused by Vibrio bacteria (1). These aquatic bacteria are found in coastal or estuarine environments as part of the natural flora but can become highly concentrated in filter-feeding sea life, including shellfish such as oysters (2, 3). Because oysters are often consumed raw or undercooked, vibrios concentrated within the oysters remain viable and infectious. Reported infections from food-borne Vibrio spp. are on the rise and are currently at the highest level since tracking began (4). While no fewer than 12 species of Vibrio are capable of infection, the 2 most common in the United States are Vibrio parahaemolyticus and Vibrio vulnificus, which cause the most infections and the most deaths, respectively (5-7). Symptoms associated with infections caused by these two species range from gastroenteritis to grievous wound infections or primary septicemia, with case fatality rates as high as 50% (2, 7-11).Both of these important bacterial species have been reported to exhibit seasonality, with warmer water temperatures resulting in increased Vibrio occurrence and concentrations in oysters (12-15). As a consequence, more than 75% of the infections caused by Vibrio spp. in the United States are observed between May and October (14). While no maximum environmental temperature has been reported, the minimum water temperature needed for the isolation of culturable V. vulnificus from oysters differs among studies but is most often reported in the range of 12 to 17°C; however, lower temperatures have also been documented in individual studies (3,12,13,(15)(16)(17)(18)(19)(20). Similarly, V. parahaemolyticus can grow in culture at a minimum temperature of approximately 10°C (21). The typical minimum water temperatures associated with oyster-related human disease reported for V. vulnificus and V. parahaemolyticus are ca. 20°C and 15°C, respectiv...

“…Predictably, the incidence of wound infections has been found to be positively correlated with warm temperatures (16,33). Because nearly all septicemia cases are associated with the consumption of raw eastern oysters (46), it has been possible to establish a risk assessment model for this pathogen in the eastern oyster (15,49). However, on the basis of epidemiological data, a direct, robustly documented linkage between the specific source of the pathogen and subsequent manifestation of V. vulnificus-associated wound infection has not been well documented in all cases (10,21,35,38).…”

mentioning

confidence: 99%

Prevalence and Population Structure of Vibrio vulnificus on Fishes from the Northern Gulf of Mexico

Tao

Larsen

Bullard

et al. 2012

The prevalence of Vibrio vulnificus on the external surfaces of fish from the northern Gulf of Mexico was determined in this study. A collection of 242 fish comprising 28 species was analyzed during the course of 12 sampling trips over a 16-month period. The prevalence of V. vulnificus was 37% but increased up to 69% in summer. A positive correlation was found between the percentages of V. vulnificus-positive fish and water temperatures, while salinity and V. vulnificus-positive fish prevalence were inversely correlated. A general lineal model (percent V. vulnificus-positive fish ‫؍‬ 0.5930 ؊ 0.02818 ؋ salinity ؉ 0.01406 ؋ water temperature) was applied to best fit the data. Analysis of the population structure was carried out using 244 isolates recovered from fish. Ascription to 16S rRNA gene types indicated that 157 isolates were type A (62%), 72 (29%) were type B, and 22 (9%) were type AB. The percentage of type B isolates, considered to have greater virulence potential, was higher than that previously reported in oyster samples from the northern Gulf of Mexico. Amplified fragment length polymorphism (AFLP) was used to resolve the genetic diversity within the species. One hundred twenty-one unique AFLP profiles were found among all analyzed isolates, resulting in a calculated Simpson's index of diversity of 0.991. AFLP profiles were not grouped on the basis of collection date, fish species, temperature, or salinity, but isolates were clustered into two main groups that correlated precisely with 16S rRNA gene type. The population of V. vulnificus associated with fishes from the northern Gulf of Mexico is heterogeneous and includes strains of great virulence potential.