Practical laboratory test for the identification of Pseudomonas aeruginosa.

Despite the efforts made to identify Pseudomonas aeruginosa by saccharolytic methods, this gram-negative microorganism remains predominately a proteolytic bacillus with weak saccharolytic activity. Pigmentation, growth temperature, pellicle formation and other minor characteristics are unsatisfactory laboratory diagnostic criteria (Gaby, 1946, 1955; Gaby and Free, 1953). Needless to say it is highly probable that numerous P. aeruginosa and P. aeruginosa-like cultures have been erroneously identified. This is undesirable not only from a diagnostic point of view but one has only to examine the classification of this genus to understand the taxonomical problems involved. The need for a diagnostic procedure which can be carried out routinely in the laboratory for the identification of nonpigmented strains of P. aeruginosa is obvious. Preliminary experiments carried out in this laboratory indicated that while the cells of P. aeruginosa contain a peroxidase and catalase, other gram-negative bacilli similar to P. aeruginosa contain similar enzymes which makes their utilization in a practical laboratory test extremely difficult. However, it appeared that P. aeruginosa contained an abundance of cytochrome oxidase. This enzyme, also referred to as Atmungsferment, indophenol oxidase, nadi oxidase, cytochrome c oxidase, cytochrome a3 oxidase, and cytochrome a oxidase, will oxidize dimethyl-p-phenylenediamine in the presence of molecular oxygen and cytochrome c, and upon the addition of a-naphthol, indophenol blue is formed. Keilin (1929) and Frei et al. (1934) have shown that several fungi and bacteria contain a cytochrome-cytochrome oxidase system. (See also the reviews by Smith, 1954; Clark et al., 1955.) The vast majority of the studies on these compounds, however, have been carried out with extracts of animal tissue in an attempt to characterize the various components of the enzymes (Wainio and Cooperstein, 1956; Estabrook, 1956; Henderson and Rawlenson, 1956; Holton, 1955; Smith and Stotz, 1954). These techniques have been modified and applied toward a practical laboratory test for the identification of P. aeruginosa.