Phenotypic Heterogeneity of Pseudomonas aeruginosa Populations in a Cystic Fibrosis Patient

Abstract

The opportunistic pathogen Pseudomonas aeruginosa chronically infects the lower airways of patients with cystic fibrosis. Throughout the course of infection this organism undergoes adaptations that contribute to its long-term persistence in the airways. While P. aeruginosa diversity has been documented, it is less clear to what extent within-patient diversity contributes to the overall population structure as most studies have been limited to the analysis of only a few isolates per patient per time point. To examine P. aeruginosa population structure in more detail we collected multiple isolates from individual sputum samples of a patient chronically colonized with P. aeruginosa. This strain collection, comprised of 169 clonal isolates and representing three pulmonary exacerbations as well as clinically stable periods, was assayed for a wide selection of phenotypes. These phenotypes included colony morphology, motility, quorum sensing, protease activity, auxotrophy, siderophore levels, antibiotic resistance, and growth profiles. Each phenotype displayed significant variation even within isolates of the same colony morphotype from the same sample. Isolates demonstrated a large degree of individuality across phenotypes, despite being part of a single clonal lineage, suggesting that the P. aeruginosa population in the cystic fibrosis airways is being significantly under-sampled.

Pseudomonas aeruginosa In VitroPhenotypes Distinguish Cystic Fibrosis Infection Stages and Outcomes

“…These characteristics represent potential possibilities for future studies. Also, recent analyses showed that traditional culture methods (i.e., isolating a small number of morphologically different bacterial colonies from each culture) frequently underrepresent the P. aeruginosa diversity in individual samples of CF respiratory secretions during chronic infection with respect to several phenotypes (44)(45)(46)(47); therefore, even the large isolate collection in this study likely undersampled the phenotypic diversity of P. aeruginosa in each subject. Similarly, it is possible that sputum and OP specimens are not sufficiently sensitive to reflect the earliest stages of infection, whether of the lower or upper airways (48,49), potentially explaining the observed high frequency in our "early" isolates of phenotypes commonly associated with adaptation.…”

Twenty-Five-Year Outbreak of Pseudomonas aeruginosa Infecting Individuals with Cystic Fibrosis: Identification of the Prairie Epidemic Strain

“…However, once PES was identified during serial assessments of patients with displacement events, unique strains were no longer observed. Furthermore, in a small sample of patients infected with PES for which morphotypic diversity was explored in great depth, coinfections were not observed (52). The identification of a high degree of concordance in infecting strains at FE and RE does not strictly rule out the possibility of a transient infection with other strains during time points not assessed.…”

“…The observed increased incidence of aminoglycoside and fluoroquinolone nonsusceptibility in PES during our study may indicate an increased treatment requirement and treatment burden in those infected with PES. PES has been demonstrated to be capable of tremendous within-patient phenotypic diversity, as measured by colony morphology, motility, protease production, auxotrophy, siderophore production, antibiotic resistance, quorum sensing, and growth patterns, similar to the within-patient heterogeneity of LES (51,52).…”

Impact of High Diversity of Achromobacter Populations within Cystic Fibrosis Sputum Samples on Antimicrobial Susceptibility Testing

“…However, CF P. aeruginosa populations were shown to be highly diverse. Indeed, in the same sputum sample, colonies that were assayed for a range of phenotypic traits, known to be altered during evolutionary adaptation, showed significant within-specimen diversity (4)(5)(6)(7). The resulting coexistence of variant lineages in the respiratory tract of CF patients suggested that they arose from diverse selection pressures in the lung and then developed distinct evolutionary pathways (5,6,8).…”