The effect of mitomycin C on the pyocine typing patterns of hospital strains of Pseudomonas aeruginosa

Abstract

With a view to shortening the time required for pyocine typing and reducing the proportion of untypable isolates, the effect of inducing strains of Pseudomonas aeruginosa by mitomycin C was studied. Detailed experiments with two strains showed that mitomycin C enhanced pyocine production by a typable strain and allowed formation of pyocine by an untypable strain. Maximal production of pyocine was achieved using mitomycin C in a concentration of 0.5 μg/ml.Three hundred and thirty-six isolates of P. aeruginosa which had been typed by Gillies and Govan's method were retyped after induction by mitomycin C. Induction and typing were performed on the same agar plate, and a 6-h incubation period at 32 °C was found sufficient for pyocine production. A similar number of typing patterns were found by both methods, but 154 isolates showed a different pattern after induction, and 23 of 38 previously untypable strains became typable. The typing patterns observed after induction were reproducible, and at least as stable epidemiologically as those obtained without induction.