Aeromonas hydrophila in livestock: incidence, biochemical characteristics and antibiotic susceptibility.

Faecal samples from 110 horses, 115 pigs, 111 sheep and 123 cows were examined for the presence of Aeromonas hydrophila, which was also sought in the available drinking water. The overall faecal rate was 11.8%, but significantly more bovine than other samples were found to be positive. There was significant association between the isolation of A. hydrophila from all animal faeces and its presence in drinking water, but this was not found when individual animal groups were analysed separately. An enrichment technique increased the total number of isolates by 77.1%. Strains of differing origins could not be differentiated by biotyping, although fermentation of sorbitol was associated with bovine isolates. There was a strong positive correlation between positive reactions for V--P, gluconate oxidase and haemolysis of rabbit erythrocytes, tests which had previously been shown to correlate with production of enterotoxin and cytotoxin. Biotypes giving positive reactions for these tests were most frequently isolated from cows, sheep and untreated water, and less frequently from pigs and horses. Most strains of A. hydrophila were resistant to amoxycillin, carbenicillin and cephradine, and sensitive to gentamicin, chloramphenicol and neomycin.