Spread of Beta-lactam-resistant Pseudomonas Aeruginosa in a Cystic Fibrosis Clinic

Background: Pseudomonas aeruginosa colonisation of the airways of patients with cystic fibrosis (CF) is associated with considerable respiratory morbidity. Although segregation of colonised patients from non-colonised patients to prevent cross-infection has been recommended, there is little evidence that such cross-infection is widespread. We observed that a high proportion of children attending our CF clinic were colonised with P aeruginosa that was resistant to ceftazidime and other beta-lactam antibiotics. We used two genomic fingerprinting techniques to see whether this may have arisen from epidemic spread of a single strain.

Methods: The prevalence of P aeruginosa colonisation and the antibiotic susceptibility of the organisms was determined from review of laboratory reports in the case-notes of 120 children with CF. Isolates were cultured from the sputum of 65 children colonised with ceftazidime-resistant P aeruginosa. Polymorphisms in total bacterial DNA from 92 isolates were analysed with two molecular fingerprinting techniques--pulsed-field gel electrophoresis after restriction enzyme digestion and assessment of flagellin gene polymorphisms by amplification of the whole gene and restriction enzyme digestion.

Results: 92 (76.7%) of 120 children were colonised with P aeruginosa, and 65 of the 92 harboured isolates that were resistant to ceftazidime. Only three of the 92 children had never been treated with ceftazidime. The results of the two molecular-fingerprinting techniques were concordant and showed that 55 of 65 children harboured the same epidemic strain. This strain was resistant to ceftazidime, azlocillin, and imipenem, and sensitive to tobramycin and ciprofloxacin.

Interpretation: This study provides the first molecular evidence of a long-term outbreak of P aeruginosa in a CF centre. We suggest that careful surveillance of the prevalence of antibiotic resistance in CF centres should be instituted with measures to prevent cross-infection. We believe that antipseudomonal monotherapy should be considered with caution.