Heterogeneity, Persistence, and Distribution of Pseudomonas Aeruginosa Genotypes in Cystic Fibrosis Patients

A collection of 222 isolates of Pseudomonas aeruginosa was obtained from the respiratory tract of 16 patients with cystic fibrosis over a 4- to 9-month period. Fourteen of these patients were unrelated, while the remaining two were siblings. Isolates were typed by conventional pyocin typing and also by the use of a DNA probe containing 741 bp immediately upstream of the exotoxin A structural gene and the initial 732 bp of the exotoxin A structural gene. By pyocin typing, 69% (11 of 16) of the patients were shown to harbor a single type that persisted in the lung throughout the study. By genotyping (DNA probe typing), all but three patients (13 of 16, 81%) harbored a single persistent genotype in their lungs. Six patients other than the sibling pair (6 of 14, 43%) shared a common genotype in their lungs as judged by DNA probing, and the pyocin type of these isolates was also identical. In four of these six patients, the shared genotype was also the persistent genotype. The sibling pair studied also carried a common genotype in their lungs as indicated by DNA probing, even though the pyocin type of these isolates varied. Results presented suggest that the majority of patients harbor a persistent strain in their lungs and that cross-colonization may occur.