Isolation medium for the recovery of Pseudomonas cepacia from respiratory secretions of patients with cystic fibrosis

Abstract

A new medium for the isolation of Pseudomonas cepacia from respiratory tract secretions of patients with cystic fibrosis (CF) is described. This medium consists of inorganic salts, 0.5% pyruvate, and 0.1% proteose peptone as nutritive components and 0.0001% crystal violet, 0.15% bile salts, 100 micrograms of ticarcillin per ml, and 300 U of polymyxin B per ml as selective agents. The medium, designated PC medium, supported superior growth of 38 of 50 stock isolates of P. cepacia after 48 h of incubation when compared with MacConkey agar (0 of 50). The medium completely inhibited the growth of 112 of 124 stock isolates of organisms commonly found in respiratory secretions of CF patients. Cultures were made on PC medium with respiratory secretions of 169 CF patients. P. cepacia was recovered from 35 patients with isolates on PC medium but from only 21 patients with isolates on MacConkey agar. Of 221 other potentially pathogenic isolates found in these specimens, only six (two Pseudomonas aeruginosa isolates, two molds, one yeast, and one Serratia marcescens isolate) grew on PC medium. PC medium should facilitate the recovery of P. cepacia from CF patients.