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Abstract:
Pseudomonas aeruginosa is an opportunistic pathogen and an important cause of infection, particularly amongst cystic
fibrosis (CF) patients. While specific strains capable of patient-to-patient transmission are known, many infections appear to
be caused by unique and unrelated strains. There is a need to understand the relationship between strains capable of
colonising the CF lung and the broader set of P. aeruginosa isolates found in natural environments. Here we report the
results of a multilocus sequence typing (MLST)-based study designed to understand the genetic diversity and population
structure of an extensive regional sample of P. aeruginosa isolates from South East Queensland, Australia. The analysis is
based on 501 P. aeruginosa isolates obtained from environmental, animal and human (CF and non-CF) sources with
particular emphasis on isolates from the Lower Brisbane River and isolates from CF patients obtained from the same
geographical region. Overall, MLST identified 274 different sequence types, of which 53 were shared between one or more
ecological settings. Our analysis revealed a limited association between genotype and environment and evidence of
frequent recombination. We also found that genetic diversity of P. aeruginosa in Queensland, Australia was indistinguishable
from that of the global P. aeruginosa population. Several CF strains were encountered frequently in multiple ecological
settings; however, the most frequently encountered CF strains were confined to CF patients. Overall, our data confirm a
non-clonal epidemic structure and indicate that most CF strains are a random sample of the broader P. aeruginosa
population. The increased abundance of some CF strains in different geographical regions is a likely product of chance
colonisation events followed by adaptation to the CF lung and horizontal transmission among patients.
