Cultural and biochemical characteristics of clinical isolates of unusual colistin-resistant pseudomonads.

Biochemical characteristics and antibiotic susceptibilities of 12 strains of colistin-resistant pseudomonads isolated from clinical specimens are reported. The isolates were short, oxidase-positive, nonfluorescing, gram-negative rods that failed to grow on salmonella-shigella or cetrimide agars, to decarboxylate amino acids, and to reduce nitrates. Most strains peptonized litmus milk and grew at 42 degrees C. Glucose, lactose, maltose, xylose, and fructose were slowly oxidized, whereas sucrose was not. Two homogeneous species were found and tentatively listed as Pseudomonas sp. 1 and Pseudomonas sp. 2, and these were differentiated by gelatin and starch hydrolysis, oxidation of mannitol, and alkalinization of allantoin. The two species were shown to differ from the Center for Disease Control Va group biotype CDC Va-1 in both biochemical characteristics and susceptibility to the aminoglycosides.