Quantitative Enumeration of Vibrio parahaemolyticus in Sea and Estuarine Waters.

Abstract

The wide distribution of Vibrio parahaemolyticus in coastal sea area has been reported by several workers in Japan. However, concerning the density of the organisms in sea water, no information has been given because of the lack of suitable method for their enumeration. A selective agar medium was deviced for this investigation and designated as AAC medium had the composition as shown in Table 1. Majority of V. parahaemolyticus utilizes arabinose as a carbon source and produces typical yellow colonies on AAC medium at 42°C, whereas most of closely related species can produce only greenish minute colonies and furthermore, the growth of usual marine flora can be inhibited. After appropriate quantities of water sample were filtered through millipore filters, the filters were incubated on the AAC medium for 16-24 hours at 42°C. All typical yellow col-onies appeared on the filters were counted as colonies of V. parahaemolyticus. A certain number of the typical colonies were picked at random from each millipore filter and the isolates were subjected to certain microscopic and biological examination for V. parahaemolyticus. In this investigation approximately 89 per cent of the isolates tested were proved to be V. parahaemolyticus as shown in Table 6. Using this procedure, the numbers of the organisms in pelagic and coastal sea waters, and estuarine waters were determined. None of the organism was isolated in the pelagic sea water samples even with 1000ml volume of them. On the other hand, it was revealed that coastal sea waters or estuarine waters con-tain 100-105 of V. parahaemolyticus per 1000ml in summer season.