Typing of Pseudomonas cepacia by bacteriocin susceptibility and production

Abstract

The significance of Pseudomonas cepacia as an opportunistic pathogen in immunocompromised patients has become increasingly recognized. Particularly disturbing is its increased incidence, reported by several North American centers, in respiratory tract cultures from patients with cystic fibrosis. Epidemiological studies of P. cepacia have been hampered by a lack of typing methods. In this paper we report the development of a typing scheme based on bacteriocin production and susceptibility. For bacteriocin production, test isolates of P. cepacia were rapidly applied to the surfaces of agar plates with a multiple inoculator. After incubation of these test isolates for 5.5 h and their exposure to chloroform, indicator strains were applied in agar overlays without prior removal of the test strain growth. After 18 h of incubation, inhibition zones caused by bacteriocin activity were recognized. A similar procedure was used to examine the bacteriocin susceptibility of the test strain. The bacteriocin type of the test strain was defined based on its bacteriocin production as judged by zones of inhibition against a set of eight indicator strains and by susceptibility or resistance of the test strain to bacteriocin produced by six producer strains. Of 373 strains of P. cepacia, 95.2% were typed into a total of 44 type combinations. Bacteriocin typing provided a suitable procedure for epidemiological studies of colonization or infection by P. cepacia. The technique described in this paper was simple to perform, gave a result within 24 h, provided good strain discrimination, and was suitable for clinical, environmental, and phytopathogenic strains.