A rapid test for Proteus species.

Rapid identification of Proteus species can represent a significant saving of time in the medical bacteriology laboratory. It is usually 2 days from receipt of the specimen to the reading of the differential slant. At this point, it is customary to inoculate one of the urea media (Edwards and Ewing, Identification of Enterobacteriaceae, Burgess Publishing Co., Minneapolis, 1955), read the result the following day, and then proceed with generic identification. Rapid urease tests have been described (Stuart, VanStratum, and Rustigian, J. Bacteriol. 49:435, 1945) and can be employed to identify Proteus species within 1 hr. The following procedure, modified from Shaw and Clarke (J. Gen. Microbiol. 13:155, 1955), may be employed to identify Proteus species from differential slants within 10 min, thereby speeding generic diagnosis by 1 day. The procedure is based on the presence of phenylalanine oxidase in Proteus species and the apparent absence of this enzyme from other enteric bacteria tested. A 0.4% solution of DL-phenylalanine (reagent grade) is sterilized by autoclaving. Solutions (10%) of H2SO4 and FeCI3 are prepared in sterile distilled water; all three reagents are kept on the laboratory bench. To carry out the test, approximately 1 ml of the sterile phenylalanine solution is added to a 10 by 75 mm Kahn tube or similar, small, sterile test tube; a large (4 mm) loopful of the organism to be tested is taken from the differential slant and emulsified in the amino acid solution. The suspension is incubated at 37 C for 10 min. To the colorless suspension are added 2 drops or 0.1 ml of the H2SO4 solution and, after shaking, 2 drops or 0.1 ml of the FeCl3 solution. The appearance of a green color, without regard to intensity of color, constitutes a positive test (for phenylpyruvic acid) and characterizes the organism under test as a member of the genus Proteus. Shaw and Clarke (J. Gen. Microbiol. 13:155, 1955) employed a 1-hr incubation period in a buffered solution of the amino acid and found that all of 118 cultures of Proteus and Providence group organisms were positive by the phenylalanine oxidase test and that 75 other cultures of Enterobacteriaceae were negative. The modification of the test proposed here has been evaluated over a 4-month period. Every Proteus species and Providence group species isolated, as well as numerous other isolates, have been tested with the following results: 68 Proteus and 2 Providence group species were positive; negative results were obtained with 76 Escherichia, 5 Paracolobactrum, 3 Salmionella, 4 A erobacter, 1 Alcaligenes, 1 Shigella, and 34 Pseudomonas species.