Pseudomonas aeruginosa in vitro phenotypes distinguish cystic fibrosis infection stages and outcomes

Abstract

Rationale: Pseudomonas aeruginosa undergoes phenotypic changes during cystic fibrosis (CF) lung infection. Although mucoidy is traditionally associated with transition to chronic infection, we hypothesized that additional in vitro phenotypes correlate with this transition and contribute to disease.

Objectives: To characterize the relationships between in vitro P. aeruginosa phenotypes, infection stage, and clinical outcomes.

Methods: A total of 649 children with CF and newly identified P. aeruginosa were followed for a median 5.4 years during which a total of 2,594 P. aeruginosa isolates were collected. Twenty-six in vitro bacterial phenotypes were assessed among the isolates, including measures of motility, exoproduct production, colony morphology, growth, and metabolism.

Measurements and main results: P. aeruginosa phenotypes present at the time of culture were associated with both stage of infection (new onset, intermittent, or chronic) and the primary clinical outcome, occurrence of a pulmonary exacerbation (PE) in the subsequent 2 years. Two in vitro P. aeruginosa phenotypes best distinguished infection stages: pyoverdine production (31% of new-onset cultures, 48% of intermittent, 69% of chronic) and reduced protease production (31%, 39%, and 65%, respectively). The best P. aeruginosa phenotypic predictors of subsequent occurrence of a PE were mucoidy (odds ratio, 1.75; 95% confidence interval, 1.19-2.57) and reduced twitching motility (odds ratio, 1.43; 95% confidence interval, 1.11-1.84).

Conclusions: In this large epidemiologic study of CF P. aeruginosa adaptation, P. aeruginosa isolates exhibited two in vitro phenotypes that best distinguished early and later infection stages. Among the many phenotypes tested, mucoidy and reduced twitching best predicted subsequent PE. These phenotypes indicate potentially useful prognostic markers of transition to chronic infection and advancing lung disease.

Keywords: epidemiology; exacerbation; mucoid Pseudomonas aeruginosa; pulmonary function; risk factors.

Figure 1.

(A) Pseudomonas aeruginosa cultures from which isolates were sampled from by age and infection stage. Each horizontal plane represents a single participant in the study cohort. (B) Prevalence of each phenotype by infection stage (corresponding percentages provided in Table E3).

Figure 2.

Results from the three multivariable models used to identify the set of phenotypes best distinguishing one infection stage from another. The set of phenotypes significantly associated with the more “advanced” infection stage as compared with the less advanced infection stage as identified using multivariable, repeated measures logistic regression. For example, reduced protease had significantly higher odds of being present during chronic infection as compared with new-onset infection (odds ratio [OR], 3.24), in addition to significantly higher odds of being present in chronic infection as compared with intermittent infection (OR, 1.95) and in intermittent infection as compared with new-onset infection (OR, 1.73). Bold phenotypes (reduced protease and pyoverdine production) showed significance across all three comparisons. C.I. = confidence interval.