Abstract
In this study, we examined the regulation of exotoxin A (ETA) production by Pseudomonas aeruginosa during chronic lung infections of cystic fibrosis (CF) patients. We used a recently developed technique termed population transcript accumulation in hybridization studies with RNA extracted from sputa. With this technique, we demonstrated that the structural gene for ETA, toxA, as well as two genes encoding positive regulators of ETA synthesis, regA and regB, were expressed in the lungs of CF patients infected with P. aeruginosa. These genes were always expressed together, never alone or in pairs, suggesting coincident expression and a possible regulatory role for regA and regB in this environment. Fluctuations in the levels of the three gene products were observed among samples, consistent with a regulatory phenomenon. The level of regB RNA detected never exceeded that of regA, although the ratio of regA RNA to regB RNA detected did change between samples. These observations are in agreement with in vitro observations which have shown that regB is located 3' to regA in an operon which is expressed from two independently regulated promoters located upstream of regA. The presence of high levels of toxA, regA, and regB RNAs in some sputum samples prompted us to look for hyperproducing-toxin strains in the sputa of CF patients. In vitro, one such strain, 4384, had a transcript accumulation pattern for toxA, regA, and regB similar to that of a laboratory hyperproducer of ETA, strain PA103. These observations suggest that regA and regB are involved in the regulation of ETA production in strains of P. aeruginosa infecting the lungs of CF patients and that some of these strains may regulate ETA production in a manner similar to that of the hyperproducing-ETA strain PA103.