Studies on Vibrio parahaemolyticus (VIII)

On “Specific” Vibrio parahaemolyticus Existing for a Long Period of Time in City River-Water

Abstract

In view of the studies on V. parahaemolyticus conducted so far by the present author, the general consideration that all of the organisms occurring in city river-water are brought directly from sea-water environments is thought to be suspectable.
Preliminary experiment indicated that the organisms could be isolated from city river-water which was allowed to stand for 24 hrs at room temperature after its collection in the daytime, and that the isolates could not survive for more than 5 hrs in the sterilized river-water.
In the present study, the similar experiment was carried out with water samples collected in the midnight from a river within the town of Nagasaki. For plating after enrichment cultivation of river water, TCBS-agar medium was employed. Consequently, the similar results (Tables 2 and 3) were obtained. These results suggest that there may be an essential difference in susceptibility to lysis in river-water between the bacterial cells before and after isolation, and lead to the assumption that “specific” V. parahaemolyticus of considerably prolonged survival may be present in natural river-water. On the other hand, it was recognized that the isolation of the organisms from river water was inhibited on BS-broth medium (Table 4). This action appears to be associated with the survival mechanism. It was also confirmed that none of the organism was detected in river water filtered through Millipore filter (Table 5). Therefore, it is unlikely that the survivors were connected with filterable cells which were previously found to occur in the culture of the organisms by the present author. There is no apparent explanation for the occurrence of “specific” V. parahaemolyticus in city river-water at the present time, though it seems possible that the organisms might exist in non-halophilic form in natural river-water before isolation.