Biochemical characteristics of enterotoxigenic Aeromonas spp.

Biotypes of Aeromonas spp. correlated well with enterotoxin production in a study of 174 strains. Using biochemical characteristics determined by conventional methods and multitest systems, we correctly classified 93% of the strains with regard to enterotoxin production. Most of the enterotoxigenic strains were Voges-Proskauer (VP) positive and did not hydrolyze arabinose, but VP-positive strains which hydrolyzed arabinose were mainly non-enterotoxigenic. Aeromonas punctata subsp. caviae, which is VP negative and does not oxidize gluconate or produce gas from glucose, was non-enterotoxigenic. Although the number of other VP-negative strains was small, most were enterotoxigenic. Discrimination was improved so that 97% of the strains were correctly classified if the hemolysin assay was used either for all strains or for only the VP-positive, arabinose-positive and VP-negative, non-A. punctata subsp. caviae strains. Because the proposed classification system does not require facilities for carrying out in vivo assays such as suckling mouse or ileal loop methods, the identification of enterotoxigenic Aeromonas strains should be possible in diagnostic laboratories and will facilitate epidemiological studies of the role of these organisms in acute diarrhea.