Opportunistic pathogens such as Pseudomonas aeruginosa are a major mortality factor for cystic fibrosis (CF) patients. Isolates of P. aeruginosa from CF patients show consistent genotypic and phenotypic changes compared to environmental and acute infection isolates, that are associated with the establishment of chronic infection. These CF isolates often exhibit reduced virulence phenotypes, which are proposed to prevent host clearance, thus supporting their persistence in the lung.
Here, we investigated the effects of long-term co-culture of P. aeruginosa with the amoeba Acanthamoeba castellanii. Co-cultures were established in low nutrient media in culture flasks (3 × independent populations), where naive A. castellanii were re-infected with amoeba-adapted P. aeruginosa populations every 3 days for 42 days. At days 3, 24 and 42, intracellular P. aeruginosa were isolated from A. castellanii. Control populations of P. aeruginosa that were not exposed to amoeba were also passaged for the same time period for comparison.
P. aeruginosa isolates exposed to A. castellanii for 42 days demonstrated decreased planktonic growth, reduced pyoverdine production and a reduction in twitching and swarming motilities. These differences were supported by genomic analysis that revealed single nucleotide polymorphisms in genes associated with pyoverdine synthesis and motility.
The phenotypic traits demonstrated by amoeba-adapted P. aeruginosa share similarities to P. aeruginosa isolates from CF lungs, suggesting that the selective factors experienced by the bacterium within amoeba are similar to those in the CF lung. Based on these data, we therefore suggest that the alteration of virulence may be a ubiquitous response of P. aeruginosa to survive the intra-host environment.