Extensive diversification is a common feature of Pseudomonas aeruginosa populations during respiratory infections in cystic fibrosis

Abstract

Background: Populations of the Liverpool Epidemic Strain (LES) of Pseudomonas aeruginosa undergo extensive diversification in the cystic fibrosis (CF) lung during long-term chronic infections.

Methods: We analyzed sets of 40 isolates from the sputa of five CF patients, each chronically infected with a different non-LES strain of P. aeruginosa. For each sample (two per patient), diversity was assessed by characterizing nine phenotypic traits.

Results: All P. aeruginosa populations were highly diverse, with the majority of phenotypic variation being due to within-sample diversity.

Conclusions: Maintenance of diverse populations in the CF lung is a common feature of P. aeruginosa infections.

Keywords: Cystic fibrosis; Population biology; Pseudomonas aeruginosa.

Supplementary Fig. 1

P. aeruginosa sub-types isolated from LES and non-LES patients. The figure shows an eBURST representation (http://eburst.mlst.net/) of all sub-types found amongst P. aeruginosa isolates from the five LES-infected and 5 non-LES infected CF patients, based on the nine phenotypic traits tested. Each dot represents a different sub-type. Sub-types differing in one characteristic are linked by a single band. The size of a dot reflects the relative abundance of the sub-type. The sub-types are arbitrarily numbered. Pink numbers represent sub-types found in both groups (LES and non-LES); Green numbers and black numbers represent sub-types found only in the LES group and non-LES group respectively.

Fig. 1

Comparisons between non-LES and LES samples. (a) Diversity within LES and non-LES samples is calculated from the probability of two isolates within a sample being of the same sub-type (p_share). Circles and triangles represent samples from the beginning and end of an exacerbation, respectively. No statistically differences in diversity were observed, either between non-LES and LES samples or between samples from the beginning versus end of an exacerbation. (b) Similarity between pairs of samples taken from the same patient. Similarity is calculated from the probability of two isolates from different samples being of the same haplotype (p_share). Circles represent pairs of samples taken at the beginning and end of an exacerbation and, hence, less than one month apart. Triangles represent pairs of samples taken at the beginning of separate exacerbations more than two months apart. Dotted lines indicate the mean level of similarity between samples from different patients within either the non-LES or the LES groups.