Differential diagnosis of Pseudomonas-like microorganisms in the clinical laboratory.

Three new laboratory tests are currently available for the identification of Pseudomonas aeruginosa isolated from clinical specimens. None of these procedures are specific for P. aeruginosa and cannot be used to differentiate between species within the genus. However, since P. aeruginosa is the only known human pathogen it is the only member of this genus that usually will be encountered in clinical specimens. All three tests are based on the oxidative characteristics of the organisms. Haynes (1951) suggested that the ability of pseudomonads to oxidize gluconate to keto-gluconate is a major characteristic of the genus and can be used to define P. aeruginosa more precisely when correlated with growth temperature and slime formation. Kovacs (1956) described a method in which the sensitivity of the oxidase test was increased to the extent that all 436 strains of P. aeruginosa examined by him gave quick, positive reactions while other gram-negative bacteria were either oxidase negative or gave delayed reactions. Gaby and Hadley (1957) developed a laboratory procedure based on the ability of pseudomonads to oxidize paminodimethylaniline oxalate (Difco) in the presence of molecular oxygen with the subsequent formation of indophenol blue within 10 to 30 sec following the addition of a-naphthol. The three tests were incorporated as routine procedures in our clinical laboratory and were compared not only for accuracy of results but also for simplicity of the technical procedure.