The microbial endocrinology of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a model pathogen with which to advance the notion that microbial endocrinology plays a central role in the pathogenesis of bacteria and other microbes. P. aeruginosa is a gram-negative opportunistic pathogen that can infect a variety of host species, including Arabidopsis, Drosophila, Caenorhabditis elegans, rodents, and man. Like many opportunistic pathogens, virulence expression in P. aeruginosa is not an invariant phenotype. Some investigators consider P. aeruginosa to be an accidental pathogen to man given that it does not appear to have co-evolved with the human immune system; as such it has been assumed to be rarely part of the normal commensal flora. Yet more comprehensive genome-based analyses of the human intestinal microflora suggest that P. aeruginosa is present in up to 20% of normal healthy individuals (Marshall 1991). Although primarily considered to be a nosocomial pathogen that infects the injured and immunocompromised host, P. aeruginosa appears to be the most common cause of infection-related deaths among patients with cystic fibrosis, a genetic disorder of the respiratory epithelium. In this latter host, P. aeruginosa is a chronic colonizer that can persist for many years where it often exerts only moderate virulence.