Incidence of Vibrio parahaemolyticus in and the Microbiological Quality of Seafood in North Carolina

Abstract

Microbiological analyses of 716 seafood samples over a 3-year period revealed that the microbiological quality of fresh seafood in North Carolina was generally acceptable. The mean aerobic counts (APC) and fecal coliform counts were low as was the occurrence of enteric pathogens, except for Vibrio parahaemolyticus and coagulase-positive staphylococci. Salmonella species were isolated from three samples, but the fecal coliform counts of these samples far exceeded the shellfish standard of the United States Food and Drug Administration. Coagulase-positive staphylococci were isolated in low numbers from nearly all the different types of seafoods; unpasteurized crabmeat and head-peeled shrimp samples showed the highest counts (10% of these samples had numbers which exceeded 100/g). V. parahaemolyticus occurred frequently in fresh seafood (overall 46% of the samples were positive) and its numbers showed a definite seasonal variation. No positive statistical correlation was found between the numbers of V. parahaemolyticus and the bacteriological indices, such as coliforms, fecal coliforms, enterococci and APC. Processing practices were found to influence the occurrence of V. parahaemolvticus in seafood; for example, improperly cleaned flumes were found to be a reservoir for V. parahaemolyticus in mechanical scallop processing plants. Also ‘picking’ waste ‘containers’ were found to be sources of V. parahaemolyticus in crab processing plants. Some processing practices such as heat shocking of oysters to facilitate opening were found to reduce the numbers of V. parahaemolyticus. Fifty V. parahaemolyticus isolates from different seafoods were tested for their Kanagawa reaction and all were found to be negative.