Modulation of Pseudomonas aeruginosa gene expression by host microflora through interspecies communication

TL;DR: Important contributions of the host microflora to P. aeruginosa infection by modulating gene expression via interspecies communications are suggested.

Abstract: Summary The change in gene expression patterns in response to host environments is a prerequisite for bacterial infection. Bacterial diseases often occur as an out- come of the complex interactions between pathogens and the host. The indigenous, usually non-pathogenic microflora is a ubiquitous constituent of the host. In order to understand the interactions between patho- gens and the resident microflora and how they affect the gene expression patterns of the pathogens and contribute to bacterial diseases, the interactions between pathogenic Pseudomonas aeruginosa and avirulent oropharyngeal flora (OF) strains isolated from sputum samples of cystic fibrosis (CF) patients were investigated. Animal experiments using a rat lung infection model indicate that the presence of OF bacteria enhanced lung damage caused by P. aerugi- nosa . Genome-wide transcriptional analysis with a lux reporter-based promoter library demonstrated that a 4% of genes in the genome responded to the pres- ence of OF strains using an in vitro system. Charac- terization of a subset of the regulated genes indicates that they fall into seven functional classes, and large portions of the upregulated genes are genes impor- tant for P. aeruginosa pathogenesis. Autoinducer-2 (AI-2)-mediated quorum sensing, a proposed inter- species signalling system, accounted for some, but not all, of the gene regulation. A substantial amount of AI-2 was detected directly in sputum samples from CF patients and in cultures of most non- pseudomonad bacteria isolated from the sputa. Tran- scriptional profiling of a set of defined P. aeruginosa virulence factor promoters revealed that OF and exog- enous AI-2 could upregulate overlapping subsets of these genes. These results suggest important contri- butions of the host microflora to P. aeruginosa infec- tion by modulating gene expression via interspecies communications.