Bacterial and Viral Pathogens in Live Oysters: 2007 United States Market Survey

Abstract

Two samples of market oysters, primarily from retail establishments, were collected twice each month in each of nine states during 2007. Samples were shipped refrigerated overnight to five U.S. Food and Drug Administration laboratories on a rotating basis and analyzed by most probable number (MPN) for total and pathogenic Vibrio parahaemolyticus and V. vulnificus numbers and for the presence of toxigenic V. cholerae, Salmonella spp., norovirus (NoV), and hepatitis A virus (HAV). Levels of indicator organisms, including fecal coliforms (MPN), Escherichia coli (MPN), male-specific bacteriophage, and aerobic plate counts, were also determined. V. parahaemolyticus and V. vulnificus levels were distributed seasonally and geographically by harvest region and were similar to levels observed in a previous study conducted in 1998-1999. Levels of pathogenic V. parahaemolyticus were typically several logs lower than total V. parahaemolyticus levels regardless of season or region. Pathogenic V. parahaemolyticus levels in the Gulf and Mid-Atlantic regions were about two logs greater than the levels observed in the Pacific and North Atlantic regions. Pathogens generally associated with fecal pollution were detected sporadically or not at all (toxigenic V. cholerae, 0%; Salmonella, 1.5%; NoV, 3.9%; HAV, 4.4%). While seasonal prevalences of NoV and HAV were generally greater in oysters harvested from December to March, the low detection frequency obscured any apparent seasonal effects. Overall, there was no relationship between the levels of indicator microorganisms and the presence of enteric viruses. These data provide a baseline that can be used to further validate risk assessment predictions, determine the effectiveness of new control measures, and compare the level of protection provided by the U.S. shellfish sanitation system to those in other countries.

Biochemical, Serological, and Virulence Characterization of Clinical and Oyster Vibrio parahaemolyticus Isolates

“…Together, tdh and trh are widely considered the predominant indicators of strain virulence in V. parahaemolyticus (26,37,38). This is substantiated by the prevalence of tdh and/or trh in clinical V. parahaemolyticus isolates and the infrequent detection of these virulence markers in food and environmental samples (9,27,28,35,40).…”

“…Together, tdh and trh are widely considered the predominant indicators of strain virulence in V. parahaemolyticus (26,37,38). This is substantiated by the prevalence of tdh and/or trh in clinical V. parahaemolyticus isolates and the infrequent detection of these virulence markers in food and environmental samples (9,27,28,35,40).Investigations of the in vitro virulence effects of the TDH have demonstrated its involvement in cytotoxicity, hemolytic activity, and mouse lethality (14,22). Although few studies have directly addressed the effects of TRH production on pathogenicity, the TRH is believed to act similarly to the TDH, based on genetic sequence similarity (2).…”

“…For example, illnesses are more frequently reported in the Pacific Northwest, where O4:K12, trh-positive, urease-positive strains are commonly isolated from patients, than along the Gulf Coast (12). However, the level of pathogenic V. parahaemolyticus strains in shellfish and environmental samples is lower in the Pacific Northwest than along the Gulf Coast (9,11,19,28,40). Except for the association of urease production with potentially virulent trh-positive strains (12,20), little focus has been placed on the biochemical activity of V. parahaemolyticus as a potential contributor to strain differentiation since the advent of genomics.…”

<i>Escherichia coli</i> in seafood: A brief overview

“…Considering bivalve mollusks, DePaola et al [39] analyzed oysters originated from nine US states and verified that the highest geometric mean levels of E. coli (~200 MPN/100g) were found in Gulf region oysters during the summer. Watkinson et al [40] detected cephalothin and gentamicin-resistant E. coli in oysters (Saccostrea commercialis) affected by wastewater treatment plants.…”

Impact of climate change on waterborne diseases

“…Vibriosis caused mainly by Vibrio parahaemolyticus, V. vulnificus and V. alginolyticus are among the 6 most common foodborne diseases monitored by the Foodborne Diseases Active Surveillance Network (FoodNet) in the USA, where V. parahaemolyticus in the past decade has become the main cause of gastroenteritis [58]. According to CDC, the incidence of Vibrio infections in the USA, which are also monitored by the Cholera and Other Vibrio Illness Surveillance (COVIS) system and are due to exposure to recreational water as well, was 76% higher in 2011 than in 1996-1998 [59].…”