Decreased baseline beta-lactamase production and inducibility associated with increased piperacillin susceptibility of Pseudomonas cepacia isolated from children with cystic fibrosis.

The incidence of pulmonary infections in children with cystic fibrosis caused by Pseudomonas cepacia, an organism which may possess an inducible beta-lactamase, has increased since 1978. Seven of 13 sputum isolates of P. cepacia from children with cystic fibrosis were classified as inducible by quantitative enzyme production following preincubation with 100, 200, or 400 micrograms/ml of cefoxitin. The recovery of inducible strains tended to be associated with recent ceftazidime therapy. Susceptibility to aztreonam, ceftazidime, and piperacillin alone or combined with the beta-lactamase inhibitors. YTR 830 or sulbactam, and isoelectric focusing for beta-lactamase were performed. Inducible isolates produced significantly more beta-lactamase than noninducible strains with or without the addition of cefoxitin. Noninducible isolates were more susceptible than inducible isolates to 8 micrograms/ml of piperacillin, a difference that was eliminated with the addition of either beta-lactamase inhibitor. Twelve of 13 strains produced a beta-lactamase band in the pH range of 7.9-8.1; no differences in satellite patterns were noted between the two groups of organisms. Increased production of beta-lactamase in the absence of an inducer may account for piperacillin resistance in P. cepacia in children with cystic fibrosis.