A transcriptome analysis of the in vitro response of Pseudomonas aeruginosa to polymorphonuclear leukocyte exposure

Polymorphonuclear leukocytes (PMNs) are a central part of the human innate immunity and they are dominating the response against bacterial infections in the cystic fibrosis (CF) lung. However, the opportunistic pathogen Pseudomonas aeruginosa can evade destruction by PMNs and may thus cause persistent infections in immuno-compromised patients. In the present in vitro study, interactions between P. aeruginosa (in the sessile and planktonic modes of growth) and PMNs were analyzed by means of DNA microarray based transcriptomics. We found that the P. aeruginosa wild type biofilms, in contrast to planktonic cultures and quorum sensing (QS) deficient strains, respond to PMN exposure in a rather aggressive manner. The response does not involve protective mechanisms such as those involved in oxidative stress. Rather it is dominated by an up-regulation of QS controlled virulence determinants such as those encoded by pqs, phz, rhlAB, lecB and lasB, all of which are able to cripple and eliminate eukaryotic cells. Our data supports a model by which P. aeruginosa recognizes the presence of PMN’s and channels this information through the QS system. Consequently, it strengthens the view that QS plays a key role in P. aeruginosa recognition and evasion of components of the host defense.