Abundance of Vibrio cholerae, V. vulnificus, and V. parahaemolyticus in Oysters (Crassostrea virginica) and Clams (Mercenaria mercenaria) from Long Island Sound

Abstract

Vibriosis is a leading cause of seafood-associated morbidity and mortality in the United States. Typically associated with consumption of raw or undercooked oysters, vibriosis associated with clam consumption is increasingly being reported. However, little is known about the prevalence of Vibrio spp. in clams. The objective of this study was to compare the levels of Vibrio cholerae, Vibrio vulnificus, and Vibrio parahaemolyticus in oysters and clams harvested concurrently from Long Island Sound (LIS). Most probable number (MPN)-real-time PCR methods were used for enumeration of total V. cholerae, V. vulnificus, V. parahaemolyticus, and pathogenic (tdh ؉ and/or trh ؉ ) V. parahaemolyticus. V. cholerae was detected in 8.8% and 3.3% of oyster (n ‫؍‬ 68) and clam (n ‫؍‬ 30) samples, with levels up to 1.48 and 0.48 log MPN/g in oysters and clams, respectively. V. vulnificus was detected in 97% and 90% of oyster and clam samples, with median levels of 0.97 and ؊0.08 log MPN/g, respectively. V. parahaemolyticus was detected in all samples, with median levels of 1.88 and 1.07 log MPN/g for oysters and clams, respectively. The differences between V. vulnificus and total and pathogenic V. parahaemolyticus levels in the two shellfish species were statistically significant (P < 0.001). These data indicate that V. vulnificus and total and pathogenic V. parahaemolyticus are more prevalent and are present at higher levels in oysters than in hard clams. Additionally, the data suggest differences in vibrio populations between shellfish harvested from different growing area waters within LIS. These results can be used to evaluate and refine illness mitigation strategies employed by risk managers and shellfish control authorities. The incidence of vibriosis in the United States has increased over the past decade (1), and it continues to be a leading cause of seafood-borne illnesses in this country (2). Among the most common causes of seafood-associated vibriosis are Vibrio cholerae (nontoxigenic), Vibrio vulnificus, and Vibrio parahaemolyticus (1, 2). Nontoxigenic (non-O1/non-O139) V. cholerae lacks the major virulence factor, cholera toxin, associated with the disease cholera (3). Infection by these strains typically results in a relatively mild form of gastroenteritis (4), but certain serotypes can cause a cholera-like illness (5, 6). Similarly, infections by the leading cause of vibriosis, V. parahaemolyticus, typically manifest as mild to moderate gastrointestinal illness (2, 7). While there is still much uncertainty surrounding V. parahaemolyticus virulence, the presence of the thermostable direct hemolysin (tdh) and tdh-related (trh) genes is commonly recognized as an indicator of pathogenicity (8,9). Although it is a less frequent cause of vibriosis, V. vulnificus can cause more severe illness, including septicemia and death, particularly in individuals with predisposing conditions (2, 10).In addition to the apparent effects of an expanding geographical range of vibrios (11), there is evidence that hard-shelled clams (Merce...

Differences in Abundances of Total Vibrio spp., V. vulnificus, and V. parahaemolyticus in Clams and Oysters in North Carolina

“…than did oysters. A study by Jones et al (23) that was conducted in Long Island Sound also found that the levels of these human pathogens, as well as Vibrio cholerae, were lower in clams than in oysters.…”

Season-Specific Occurrence of Potentially Pathogenic Vibrio spp. on the Southern Coast of South Korea

“…Studies conducted all over the world have highlighted the environmental factors that affect the abundance and distribution of V. parahaemolyticus, such as water salinity, temperature, turbidity, and the levels of chlorophyll and organic matter in suspension (10). Although the mechanism underlying human infection by V. parahaemolyticus is not completely understood, there are two hemolysins that are commonly recognized as pathogenicity indicators: thermostable direct hemolysin (TDH), which is a pore-forming protein involved in bacterium invasion, and TDH-related hemolysin (TRH), which plays a significant role in virulence (10)(11)(12). Most of the clinical isolates of V. parahaemolyticus possess tdh and/or trh; however, a relatively low number of environmental isolates were found to carry these genes (10,13).…”

Vibrio bacteria in raw oysters: managing risks to human health

“…Intriguingly, temperature was not significantly related to concentrations of pathogenic strains [32,39]. By contrast, Jones et al [36] observed that when temperature did not affect total concentrations of V. parahaemolyticus, it did have an effect on tdh-and trh-positive strains.…”

“…For V. vulnificus, most studies find that temperature drives bacterial concentrations [25][26][27][28][29][30][31][32][33][34], V. vulnificus most easily being isolated in oyster tissues with a temperature range from 158C to 178C [26,27,29,32]. Exceptions include Parvathi et al [35], Jones et al [36] and Givens et al [37], though a common limitation to these studies is a lack of variation in temperature over the sampling period. Models assume that salinity does not play a factor in V. vulnificus abundance, but reported effect of salinity on V. vulnificus varies from location to location, including insignificant [25,30,32,37], positive [29], inhibitory [26,28,31,38] or nonlinear [27] associations.…”