Ecology of Vibrio species, including Vibrio cholerae, in natural waters of Kent, England

The distribution of Vibrio species in water from two sites in Kent was studied between 1978 and 1980. They were counted by a most probable number technique using alkaline peptone water for enrichment followed by plating onto thiosulphate citrate bile salt sucrose agar, or by direct plating of water onto the same agar. In a freshwater stream both upstream and downstream from a human sewage works outfall V. metschnikovii was the predominant Vibrio. Vibrio anguillarum was isolated sporadically. Non-O1 serovars of V. cholerae occurred only twice. At the other site in a ditch containing static, brackish water, non-O1 V. cholerae (highest number 400 cfu/ml) was observed as present only from May to November. Vibrio anguillarum was isolated throughout the sampling period. The presence of non-O1 V. cholerae in both sites was not dependent on the input of human sewage. The hypothesis that non-toxigenic V. cholerae can survive and multiply in water was tested in the ditch by the use of submersible chambers constructed of polycarbonate membranes and Plexiglass. The seasonal incidence of non-O1 V. cholerae in the brackish water site could be explained by the multiplication of the organism when the water temperature exceeded 9°C. It was concluded that strains of V. cholerae that are unable to produce cholera toxin are indigenous to static brackish water environments and the possibility that this applies to toxigenic strains as well should be investigated.