Marked phenotypic variability in Pseudomonas cepacia isolated from a patient with cystic fibrosis

Characterization of the epidemiology of Pseudomonas cepacia colonization in cystic fibrosis is difficult because of the phenotypic variability of isolates. A single sputum culture may yield colonies which differ in morphology, antibiotic susceptibility, and pigment production. We examined serial P. cepacia isolates from a cystic fibrosis patient which the clinical laboratory identified as separate strains; these were selected on the basis of isolation date and culture site. An attempt was made to sample at multiple time points and, at a single time point, from three different culture sites. Ribotype analysis, using both the standard Southern blot technique and a recently reported method which uses the polymerase chain reaction, was used to distinguish unique P. cepacia strains. Characterization included comparison of antibiotic susceptibility, plasmid content, and outer membrane protein (OMP) patterns. rRNA analysis demonstrated that all isolates had the same ribotype, consistent with their being derivatives of the same strain. Antibiotic susceptibility testing revealed variability among both same-date and same-site isolates. Screening for plasmid DNA identified three groups of isolates; both same-date and same-site isolates demonstrated variability. OMP profiles were similar, but at least six distinct patterns were identified. For the six same-date isolates, five different OMP patterns were identified. For the 10 same-site isolates from different dates, five of the six OMP patterns were represented. We have demonstrated marked phenotypic variability in 14 strains of P. cepacia isolated from different sites and at different times from a single colonized patient. Ribotyping identified all the isolates as derivatives of a single strain; thus, the diversity of phenotypes appears to be the result of differential gene expression.