ASSOCIATION BETWEEN TRANSCRIPT LEVELS OF THE PSEUDOMONAS-AERUGINOSA REGA, REGB, AND TOXA GENES IN SPUTA OF CYSTIC-FIBROSIS PATIENTS

In this study, we examined the regulation of exotoxin A (ETA) producti on 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 e xtracted from sputa. With this technique, we demonstrated that the str uctural gene for ETA, toxA, as well as two genes encoding positive reg ulators of ETA synthesis, regA and regB, were expressed in the lungs o f CF patients infected with P. aeruginosa. These genes were always exp ressed together, never alone or in pairs, suggesting coincident expres sion and a possible regulatory role for regA and regB in this environm ent. Fluctuations in the levels of the three gene products were observ ed among samples, consistent with a regulatory phenomenon. The level o f regB RNA detected never exceeded that of regA, although the ratio of regA RNA to regB RNA detected did change between samples. These obser vations are in agreement with in vitro observations which have shown t hat regB is located 3' to regA in an operon which is expressed from tw o independently regulated promoters located upstream of regA. The pres ence of high levels of toxA, regA, and regB RNAs in some sputum sample s prompted us to look for hyperproducing-toxin strains in the sputa of CF patients. In vitro, one such strain, 4384, had a transcript accumu lation pattern for toxA, regA, and regB similar to that of a laborator y hyperproducer of ETA, strain PA103. These observations suggest that regA and regB are involved in the regulation of ETA production in stra ins of P. aeruginosa infecting the lungs of CF patients and that some of these strains may regulate ETA production in a manner similar to th at of the hyperproducing-ETA strain PA103.