Isolation of Aeromonas spp. from an unchlorinated domestic water supply

The recovery of Aeromonas spp. from the unchlorinated water supply for a Western Australian city of 21,000 people was monitored at several sampling points during a period of 1 year. Membrane filtration techniques were used to count colonies of Aeromonas spp., coliforms, and Escherichia coli in water sampled before entry to service reservoirs, during storage in service reservoirs, and in distribution systems. Aeromonas spp. were identified by subculture on blood agar with ampicillin, oxidase tests, and the use of Kaper medium and then were tested for production of enterotoxins and hemolysins. During the same period, two-thirds of all fecal specimens sent for microbiological examination were cultured on ampicillin-blood agar for Aeromonas spp. Recovery of Aeromonas spp. from water supplies at distribution points correlated with fecal isolations and continued during autumn and winter. Coliforms and E. coli were found most commonly in late summer to autumn. This pattern differs from the summer peak of Aeromonas isolations both from water and from patients with Aeromonas spp.-associated gastroenteritis in Perth, Western Australia, a city with a chlorinated domestic water supply. Of the Aeromonas strains from water, 61% were enterotoxigenic, and 64% produced hemolysins.