Expression data from Pseudomonas aeruginosa (wild type and lasRrhlR mutant strains) exposed to human neutrophils

In the present in vitro study, interactions between P. aeruginosa (sessile biofilms as well as planktonic cells) 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 QS controlled virulence determinants such as those encoded by pqs, phz, rhlAB, all of which are designed to cripple Eukaryotic cells including PMNs and macrophages. Our comparative analysis supports the view that QS plays a major role in mechanisms by which P. aeruginosa evades host defense systems. Keywords: Stress response The biofilms were allowed to grow and develop in the biofilm flow chambers for 3 days before challenge with PMNs. Fresh PMNs from human volunteers were isolated and resuspended in RPMI-1640 medium (BIOCHROM AG) as previously described by Bjarnsholt et al. 2005 (Bjarnsholt et al., 2005). Prior to PMN injection the flow was halted. Ten million PMNs were resuspended in 6 ml of RPMI media and injected into the flow chamber. The concentration of PMNs was found by microscopy to be approximately 1 PMN per 1000 bacterial cells. PMNs and biofilm were incubated for 2 hours. The flow chambers were rolled every 15 minutes to ensure that the entire biofilm was exposed to the PMNs. After incubation the fluid inside the chamber was discarded and the attached biofilm cells were loosened by rolling. The cells were then mechanically removed and collected in 6 ml of RNAlater®