Molecular detection of an atypical, highly resistant, clonal Pseudomonas aeruginosa isolate in cystic fibrosis patients.

BACKGROUND The identification of Pseudomonas aeruginosa (P. aeruginosa) isolates in sputum from cystic fibrosis (CF) patients can be challenging due to the multitude of phenotypic changes isolates undergo during adaptation to the microenvironment of the CF lung. METHODS We report the occurrence of shared P. aeruginosa isolates which failed identification by phenotypic methodologies and required species specific polymerase chain reaction. P. aeruginosa isolates were genotyped by macrorestriction analysis. RESULTS Analysis of atypical isolates revealed one clonal P. aeruginosa isolate and three smaller clusters. In contrast molecular typing of phenotypically characteristic P. aeruginosa isolates revealed only small clusters. Despite exhibiting higher levels of antimicrobial resistance, acquisition of atypical strains was not associated with significant changes in clinical decline. CONCLUSIONS Our experience highlights the importance of accurate identification of bacterial isolates in CF lung disease to detect clonal spread of atypical isolates.