Determination of Pseudomonas aeruginosa by Biochemical Test Methods

II. Acylamidase Test, a Modified Biochemical Test for the Identification of Pseudomonas aeruginosa

Abstract

A rapid and simple test method for the detection of acylamidase activity of Pseudomonas aeruginosa was devised. One loopful of a nutrient agar overnight culture of a test organism was inoculated into 1 ml of a test medium consisting of 0.2% KH₂PO₄, 0.01% MgSO₄·7H₂O, 0.5% NaCl and 0.1% acetamide (final pH 6.8). After aerobic incubation at 37C for 6 hr, one drop of Nessler's reagent was dropped into the test medium. A reddish-brown sediment appeared immediately if results were positive. Of 40 test strains of P. aeruginosa 39 gave strongly positive results. A strain showed a weakly positive result after 6 hr incubation, but the reaction became stronger after 18 hr culture. Other species of Pseudomonas, and various species of bacteria such as genera Vibrio and Aeromonas, and family Enterobacteriaceae were negative in this test. From these experimental results, the acylamidase test was considered to be highly specific for strains of P. aeruginosa, and therefore useful as a reliable method for the identification of this species.