No abstract

We used DNA restriction fragments, derived from the exotoxin A gene and surrounding sequences, as an epidemiological marker for Pseudomonas aeruginosa. Using these DNA fragments as probes in Southern blot hybridizations and/or total genomic digestions, we were able to distinguish greater than 100 different strains of P. aeruginosa. The stability of the marker in vitro was established by using well-characterized strains, which were stored under different conditions and subjected to chemical mutagenesis. The stability of the marker within a given strain in vivo was established during experimental infection in the chronic rat lung model of pseudomonas pneumonia. P. aeruginosa serially cultured from individual patients with cystic fibrosis were examined by using this marker. Isolates that varied in colonial morphology, serotype, and biotype were identical when analyzed by Southern blot hybridization using the fragment as a probe. Indistinguishable isolates (by serotyping, biotyping, and antibiograms) cultured from two unrelated patients were easily distinguished by using Southern blot analysis.

SUMMARYTo investigate cross-colonization with and persistence of Pseudomonas aeruginosa in cystic fibrosis (CF), 181 isolates from 76 CF patients were typed using a P. aeruginosa-specific DNA probe. Whereas sibling pairs predominantly harboured genotypically identical P. aeruginosa strains, all of the other patients harboured different strains. Seventy-nine per cent (22/31) of the infected CF patients harboured the same strains at the beginning and the end of a summer camp. A change of strains was seen in 10% (3/31) of the patients at the end of the camp. Forty-six per cent (6/13) of the patients who were apparently initially uninfected, acquired P. aeruginosa by the end of the period. Genotyping proved that strain change or acquisition was due to cross-colonization in four of nine cases. Very little P. aeruginosa was isolated from the inanimate environment. Persistence of P. aeruginosa after a temporary loss due to antibiotic therapy was seen in 12/16 paired patient strains before and after antibiotic therapy. Thus, suppression followed a flare-up seemed to occur in these patients rather than eradication and a new infection. When 35 patients were followed over a period of 6 months, 7 (20 %) changed the strain in their sputum. Only one of 43 patients harboured two different P. aeruginosa strains simultaneously over a long period.