Uptake and Retention ofVibrio choleraeO1 in the Eastern Oyster,Crassostrea virginica†

Vibrio choleraeO1, the causative agent of cholera, is known to persist in estuarine environments as endogenous microflora. The recent introduction of V. cholerae O1 into estuaries of the North and South American continents has stimulated the need to determine the effect of controlled purification on reducing this pathogen in edible molluscan shellfish. Experiments defined parameters for the uptake and retention ofV. choleraeO1 in tissues of Crassostrea virginica, and these parameters were compared with those for Escherichia coli and Salmonella tallahassee, bacteria which are usually eliminated from moderately contaminated shellfish within 48 h.OystersaccumulatedgreaterconcentrationsofV.choleraeO1thanE.coliandS.tallahassee.WhenV.cholerae O1 was exposed to controlled purification at 15, 19, and 25&C over 48 h, it persisted in oysters at markedly higher levels thanE. coliand S. tallahassee. The concentration of aV. choleraeO1-specific agglutinin did not positively correlate with the uptake or retention of V. cholerae O1. These data show that state and federally approved controlled purification techniques are not effective at reducingV. choleraeO1 in oysters. It is estimated that 1 in 2,000 meals of raw molluscan shellfish results in disease (19), making these shellfish one of the most hazardous foods (22, 34). Such risk is related to the high numbers of microorganisms that oysters accumulate from overlying waters (11, 18‐20) and the consumption by humans of the entire animal in a raw or undercooked form. Risk is further enhanced by pollution of shellfish growing waters, during product handling from harvest to retail market, and by compromised host defenses of the consumer. Of the numerous human diseases that can be transmitted by oysters, cholera is a significant cause of morbidity worldwide (4).Vibrio choleraeO1, the etiological agent (3, 6, 31), is easily spread over large geographical areas by water, infected travelers, and imported seafoods. Once the bacterium is endemic, bothfreshandestuarinewatersandplanktoncanbereservoirs ofV. choleraeO1 and vectors of seafood disease (29). Such a situation was recently realized during the epidemic ofV. choleraeO1 in Latin America, where very high levels ofV. cholerae O1 have been reported in Peruvian environments (31). This intensifies the need to investigate interactions between this pathogen and shellfish and to determine possible methods for reducing its numbers. A state and federally approved postharvest process termed controlled purification (depuration) can increase the safety of shellfishproducts(21).Itcanreducethenumberofpathogenic organisms present in shellfish harvested from moderately polluted (restricted) waters to levels acceptable for human consumption (35). However, the effect of depuration on V. choleraeO1 is not understood. Research to determine the efficacy of the process and the specific factors involved in the elimination ofV. choleraeO1 is needed. A factor that is hypothesized to influence the retention ofV. cholerae O1 in oysters is a V. cholerae O1 agglutinin found in oyster hemolymph and on the surface of oyster tissues (28). This agglutinin reacts with all serotypes and biotypes of V. choleraeO1 and has been demonstrated in oysters (i.e.,Crassostrea virginica) from different environments along the Gulf and Atlantic coasts (28). It remains to be determined whether the presence or absence of this V. cholerae O1 agglutinin affects the persistence ofV. choleraein oyster tissues.