Isolation of Aeromonas hydrophila from Bottled Waters and Domestic Water Supplies in Saudi Arabia

Abstract

A total of 139 replicate samples of water were tested for Aeromonas hydrophila and coliforms. These consisted of 95 replicates from bottled mineral water, 13 replicates from flower petal infusions and 31 samples of domestic municipality supplies. Of these, 59 (43%) were positive for A. hydrophila, 15 (11%) were positive for coliforms and 11 (8%) positive for both A. hydrophila and coliforms. Most of the isolates of A. hydrophila came from various batches of one brand of bottled mineral water, none of which contained coliforms. The organism was isolated more frequently from newer samples, particularly those bottled for 59 d or less. Samples of treated water from one municipality were free from coliforms and A. hydrophila. Chlorinated water from another town was free from coliforms, but some samples contained A. hydrophila. In unchlorinated water from a third municipal source, there was a high degree of correlation between incidence of A. hydrophila and presence of coliforms. A selective method, using media without antibiotics, for isolation of A. hydrophila was used. A novel medium for the presumptive identification of A. hydrophila, gelatin arginine dihydrolase (GAD) medium, was assessed, with confirmation of suspected isolates using the API 20E system. Of 109 isolates from two selective agars identified with the organism on API strips, 18 (16.5%) were falsely gelatinase negative in GAD medium, of which 9 (8.3%) also gave false-negative arginine dihydrolase reactions. Of those presumptively identified as A. hydrophila in GAD, 4/95 isolates (4.2% false-positives) were not confirmed.