Environmental and clinical strains of Vibrio cholerae were exposed to nutrient-free artificial seawater and filtered natural seawater microcosms for selected time intervals and examined for changes in cell morphology and number. Cells observed by transmission electron and epifluorescence microscopy were found to undergo gross alterations in cell morphology with time of exposure. The vibroid cells decreased in volume by 85% and developed into small coccoid forms surrounded by remnant cell walls. The initial number of cells inoculated into nutrient-free microcosms (culturable count and direct viable count) increased 2.5 log10 within 3 days, and even after 75 days the number of viable cells was still 1 to 2 log10 higher than the initial inoculum size. Nutrient-depleted coccoid-shaped cells were restored to normal size and assumed a bacillary shape within 3 h and began to divide within 5 h after nutrient supplementation. The increase in cell number and decrease in cell volume under nutrient-depleted conditions, as well as the rapid growth response after nutrient supplementation, may describe some of the survival mechanisms of V. cholerae in the aquatic environment.

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.

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