Rapid identification of motile Aeromonas

The clinical relevance and taxonomy of motile Aeromonas species are areas of current controversy. Strains of motile Aeromonas isolates (n = 60) from various sources were identified to species level using the following tests (all incubated at 30 degrees and 37 degrees C): esculin hydrolysis; formation of gas from glucose; production of acetoin; production of acid from mannitol and arabinose; decarboxylation of lysine and ornithine, dihydrolation of arginine; and pyrazinamide hydrolysis in a semisolid medium. The tests' results were similar at incubation temperatures of 30 degrees and 37 degrees C. Of the strains, 59 (98%) of 60 were identified to species level by the full battery of tests: 25 as A. hydrophila, 18 as A. caviae, 14 as A. sobria, one as A. veronii, and one as A. schubertii. (The only A. veronii and A. schubertii isolates identified were ATCC strains). All (25 of 25) strains of A. hydrophila and 17 (94%) of 18 of A. caviae hydrolyzed pyrazinamide in less than 24 hr, whereas all strains of A. sobria showed no pyrazinamidase activity. Absence of pyrazinamidase was, thus, a convenient phenotypic marker for A. sobria. Four additional tests (esculin hydrolysis, acetoin production, lysine decarboxylation, and gas production from glucose) identified within 24 hr all examples of the three common species of Aeromonas. Recently proposed species did not contribute to our ability to discriminate among stool, other clinical, and environmental isolates of Aeromonas spp.