DIFFERENTIAL GENE-EXPRESSION BY PSEUDOMONAS-AERUGINOSA DURING INTERACTION WITH RESPIRATORY MUCUS

Pseudomonas aeruginosa is a common respiratory tract pathogen that cau ses serious infections in patients with cystic fibrosis. A number of p utative virulence factors have been characterized in several laborator ies, and some have been implicated in human infections, based on crite ria such as the phenotype of isolates from infected patients, an immun e response to a particular antigenic factor, and the effect of a virul ence factor on infectivity in an animal model. We have developed a ser ies of genetic tools to study the selective regulation of expression o f P. aeruginosa genes during interactions of the pathogen with host ti ssues. These tools are based on direct enrichment of bacteria, when a particular promoter is induced or repressed. We have found that intera ction of bacteria with mucus from patients with cystic fibrosis result s in marked induction of expression of several genes, including one th at encodes a lipopolysaccharide biosynthetic enzyme, a gene for a prot ein responsible for uptake of the ferric pyochelin siderophore, and a new gene homologous with a class of iron-responsive repressors. The to ols described here are useful for identification of induced or repress ed genes in various animal models of infection or in controlled labora tory conditions that mimic natural infections of humans. Such genes mi ght not be detectable when bacteria are cultured in laboratory conditi ons, and these tools are therefore useful for general probing of a bac terial genome for genes regulated during different stages of infection .