Seasonal Abundance of Total and Pathogenic Vibrio parahaemolyticus in Alabama Oysters

Abstract

Recent Vibrio parahaemolyticus outbreaks associated with consumption of raw shellfish in the United States focused attention on the occurrence of this organism in shellfish. From March 1999 through September 2000, paired oyster samples were collected biweekly from two shellfish-growing areas in Mobile Bay, Ala. The presence and densities of V. parahaemolyticus were determined by using DNA probes targeting the thermolabile hemolysin (tlh) and thermostable direct hemolysin (tdh) genes for confirmation of total and pathogenic V. parahaemolyticus, respectively. V. parahaemolyticus was detected in all samples with densities ranging from <10 to 12,000 g ؊1 . Higher V. parahaemolyticus densities were associated with higher water temperatures. Pathogenic strains were detected in 34 (21.8%) of 156 samples by direct plating or enrichment. Forty-six of 6,018 and 31 of 6,992 V. parahaemolyticus isolates from enrichments and direct plates, respectively, hybridized with the tdh probe. There was an apparent inverse relationship between water temperature and the prevalence of pathogenic strains. Pathogenic strains were of diverse serotypes, and 97% produced urease and possessed a tdh-related hemolysin (trh) gene. The O3:K6 serotype associated with pandemic spread and recent outbreaks in the United States was not detected. The efficient screening of numerous isolates by colony lift and DNA probe procedures may account for the higher prevalence of samples with tdh ؉ V. parahaemolyticus than previously reported.Vibrio parahaemolyticus is a gram-negative, halophilic bacterium that occurs naturally in estuarine environments worldwide (21). Its densities in the environment and seafoods vary greatly by season, location, sample type, fecal pollution, and analytical methodology (5, 8-10, 14, 21, 22, 36). Pathogenic V. parahaemolyticus generally produces a thermostable direct hemolysin (TDH), the product of the tdh gene (20). More than 90% of clinical V. parahaemolyticus isolates but fewer than 1% of food or environmental strains produce TDH or possess tdh (9,10,14,22,26,31,35). The frequency of TDH or tdh detection in environmental samples and seafoods ranges from 0 to 6% (5,14,22,26,31,34). Quantitative data for tdh ϩ V. parahaemolyticus have been reported in only one study and are based on one or two isolates from each of four oyster samples (10).A series of oyster-associated outbreaks of V. parahaemolyticus (3, 4, 6, 7) in 1997 (Washington State) and 1998 (Texas, New York and Connecticut, and Washington State) prompted the development of nonradioactive DNA probes (28, 29) and direct-plating methods for rapid and efficient determination of the abundance of total and pathogenic V. parahaemolyticus in oysters. The Food and Drug Administration (FDA) initiated a surveillance program using these new methods in Alabama in March 1999. The objective of this study was to correlate quantitative data on the abundance of total and pathogenic V. parahaemolyticus with each other and with environmental parameters such as water temperature and salini...

Occurrence of potentially pathogenic Vibrio in oysters (Crassostrea gigas) and waters from bivalve mollusk cultivations in the South Bay of Santa Catarina

“…The tdh gene was detected in four strains, and trh was detected in 23 strains (Figure 2). Several studies have suggested a strong influence of temperature on the concentration of vibrio in marine waters [27][28][29][30] . However, this study only established a correlation with V. vulnifi cus (p < 0.05).…”

Serological and molecular characterization of Vibrio parahaemolyticus marine strains carrying pandemic genetic markers

“…V. parahaemolyticusmediated gastroenteritis has traditionally been associated with two virulence factors, thermostable direct hemolysin (TDH) and TDH-related hemolysin, which are present in most clinical isolates and have been detected with low frequency in environmental strains (DePaola et al, 2003;Dileep et al, 2003). The relationship between strains isolated from the aquatic environment, considered the source of the infection, and strains isolated from clinical cases is poorly understood.…”

Biosynthesis of the Osmoprotectant Ectoine, but Not Glycine Betaine, Is Critical for Survival of Osmotically Stressed Vibrio parahaemolyticus Cells

“…In the marine and estuarine environments, V. parahaemolyticus must navigate changing salinities, temperatures, and nutrient limitations and is known to proliferate during the warmer months of the year when the salinity and temperature are elevated (2,(5)(6)(7)(8)(9). Vibrio parahaemolyticus levels in marine and estuarine waters are linearly dependent on both salinity and water temperature, and in the winter, the bacterium is rarely isolated from the water column and is typically only found in small numbers in sediment (2,5,10).…”