<i>Pseudomonas aeruginosa</i> and Cystic Fibrosis – A Nasty Bug Gets Nastier

risk of mortality that is 2–3 times higher than similar patients who are not infected with P. aeruginosa . Data from the study by Lechtzin et al. suggests that even amongst those patients already infected with P. aeruginosa , there exists a subgroup of patients infected with multiply antibiotic-resistant isolates who fare even more poorly. Why do these patients have unfavourable outcomes? It is possible, but not confi rmed in this study, that some of the patients infected with antibiotic-resistant isolates may have been infected with a clonal strain of P. aeruginosa bacteria common to the Johns Hopkins clinic. The study by Lechtzin et al. did not utilize molecular typing of isolates and it is therefore impossible to determine if these antibiotic-resistant isolates represent epidemic clones. However, studies from Australia and the UK have shown evidence of clonal epidemic strains of P. aeruginosa that have infected a majority of CF patients in certain clinics [4, 5] . One small retrospective study of 12 patients from Liverpool suggested that patients infected with the Liverpool multiresistant epidemic strain had poorer outcomes compared to 12 matched patients infected with unique strains of P. aeruginosa [6] . Why else might these patients do more poorly? Bacteria such as P. aeruginosa are known to develop antibiotic resistance through development of multidrug effl ux systems, altered membrane permeability, and plasmid-mediated resistance. Many of these bacterial resistance In this issue of Respiration Lechtzin et al. [1] describe outcomes in adult cystic fi brosis (CF) patients at the Johns Hopkins CF clinic who were infected with multiply antibiotic-resistant Pseudomonas aeruginosa (MARPA) bacteria. Of 75 adults followed in their clinic, 21 developed antibiotic-resistant P. aeruginosa during a 33-month study period and 13 were infected with antibiotic-resistant P. aeruginosa throughout the study period. The authors demonstrate using survival analyses that patients who were infected with MARPA had an increased risk of death or lung transplantation compared to those patients who were infected with antibiotic-susceptible P. aeruginosa . Multivariable analyses also suggested that these patients had more rapid declines in FEV 1 per year. P. aeruginosa has long been a scourge of CF patients and CF clinics. Approximately 70% of adults in North American CF clinics are chronically infected with P. aeruginosa . Once established, the infection is virtually impossible to eradicate in adults. Studies have shown that P. aeruginosa forms biofi lms within the CF airway, and that most adults are infected with a single clone of P. aeruginosa in their airway secretions even when multiple morphotypes are isolated from sputum [2] . Large database analyses of CF patients from the US and Canada have confi rmed that infection with P. aeruginosa is an independent risk factor for mortality [3] . Those patients infected with P. aeruginosa have a relative