Effect of Processing and Storing Oyster Meats on Concentrations of Indicator Bacteria, Vibrios and Aeromonas hydrophila

Abstract

Oyster meats were examined from three commercial processing plants at different stages of processing and storage for four standard indicator bacterial groups, five species of vibrios reported to be associated with shellfish associated gastroenteritis, and Aeromonas hydrophila. Processing reduced the overall microbial load, but the individual bacterial groups examined remained statistically the same throughout processing. Upon storage, the concentration of Vibrio parahaemolyticus significantly declined with a concomitant increase in levels of A. hydrophila, and the levels of all other Vibrio spp. remained statistically the same. The findings suggest that, while processing results in a cleaner appearing product, processing does not eliminate potentially pathogenic vibrios. However, processing and subsequent storage of oyster meats do not appear to increase the levels of vibrios.

The human pathogenic vibrios – A public health update with environmental perspectives

“…Contamination of these shellfish by pathogenic Vibrio species cannot be controlled by restricting faecal contamination of growing water so the rationale of shellfish sanitation programmes has limited application. Raw seafood and shellfish should be kept at refrigeration temperature (less than 5°C) or placed on ice immediately after harvesting or processing to prevent multiplication to numbers likely to cause disease (Hood, Baker & Singleton, 1984;Fletcher, 1985;Reily & Hackney, 1985;Saxena & Kulshrestha, 1985;Ingham & Potter, 1988). It is noteworthy that although V. vulnificus is unable to survive well in whole oysters at near-freezing temperatures (Oliver, 1981), there has been at least one reported case of infection following consumption of refrigerated raw oysters (Johnston, Andes & Glasser, 1983).…”

Starch-Ampicillin Agar for the Quantitative Detection of Aeromonas hydrophila

“…Recently, Buchanan (4) alternatively suggested that the species may represent a significant "new" food-borne pathogen and hypothesized that foods may be important in the dissemination of the microorganism. The basis for this hypothesis was the pathogenicity of the species in fish and reptiles (10), its frequent isolation from various foods of animal origin (1,3,7,8,11,12,14,15,20), and the psychrotrophic nature of the species (S. A. Palumbo, D. R. Morgan, and R. L. Buchanan, J. Food Sci., in press).…”

Current perspectives on the epidemiology and pathogenesis of clinically significant Vibrio spp.

“…The most commonly used enrichment medium for all vibrios of medical interest is alkaline peptone water. Salt colistin broth, glucose salt teepol broth, and arabinose-ethyl violet broth have been recommended for enrichment of V. parahaemolyticus but not for other species; alkaline bile peptone water has been recommended for V. cholerae but has not been evaluated for other species (40,67,69,93,183,204). Incubation times of 6 to 18 h at 35 to 370C have commonly been used for enrichment (6 h, optimum), although a new procedure designed to recover V. cholerae involves incubation in alkaline peptone water at 420C for 18 h (40).…”

“…Various studies have determined the effects of storage on the concentration of vibrios in oysters and clams, both before and after shucking (67,69). Storage of clams at the usual cold temperatures appears to have little effect on the generally low levels of vibrios present.…”