Decreased Baseline β-Lactamase Production and Inducibility associated with Increased Piperacillin Susceptibility of Pseudomonas cepacia Isolated from Children with Cystic Fibrosis

Abstract

ABSTRACT. The incidence of pulmonary infections in children with cystic fibrosis caused by Pseudomonas cepacia, an organism which may possess an inducible 8-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 pg/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 b-lactamase inhibitors. YTR 830 or sulbactam, and isoelectric focusing for /3-lactamase were performed. Inducible isolates produced significantly more /3-lactamase than noninducible strains with or wihtout the addition of cefoxitin. Noninducible isolates were more susceptible than inducible isolates to 8 pg/ml of piperacillin, a difference that was eliminated with the addition of either P-lactamase inhibitor. Twelve of 13 strains produced a Plactamase 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 /3-lactamase in the absence of an inducer may account for piperacillin resistance in P. cepacia in children with cystic fibrosis. creased since 1978 and is now recovered from 20% of patients in some centers (3, 4).Sputum isolates of P. cepacia from children with cystic fibrosis are resistant to most P-lactam agents in vitro. In an in vitro study comparing the susceptibilities of 62 consecutive sputum isolates, concentrations of 64 pg/ml of aztreonam and piperacillin were required to inhibit 79 and 87.1 % of the bacterial population, respectively; 90% of the isolates were inhibited by 8 pg/ml of ceftazidime (5). In vitro, ceftazidime has proven more active against P. cepacia than piperacillin, aztreonam, HR-810, or BMY-28 142 (5, 6). Although the mechanism(s) of resistance of P. cepacia to Plactam agents is unclear, at least three, inducible, isoelectrically distinct p-lactamases have been identified (9-1 1). Hirai et al. (10) noted that the enzyme produced by Pseudomonas cepacia GN I 1 164 hydrolyzed cefuroxime, cefotaxime, and cefamandole. The purpose of this study was to ascertain the role played by inducible enzyme production in resistance to piperacillin, aztreonam, and ceftazidime by sputum isolates of P. cepacia from patients with cystic fibrosis. MATERIALS AND METHODSTest strains. Thirteen isolates of P. cepacia recovered from the sputum of 12 children admitted to Rainbow Babies and Children's Hospital with pulmonary exacerbations of cystic fibrosis were studied. With one exception, all of the test strains were recovered between April and December 1984. Seven of the 13 test strains were recovered during or immediately after ceftazidime therapy; two isolates were recovered following ciprofloxacin therapy, one isolate after aztreonam therapy, and three isolates were obtained prior to parenteral antibiotic therapy. Pseudomonas aeruginosa ATCC 27853 was use...

Outer membrane permeability in Pseudomonas cepacia: diminished porin content in a beta-lactam-resistant mutant and in resistant cystic fibrosis isolates

“…One resistant mutant, designated 75-26Mc, was selected for this study. Strains 16901 and 619i were P-lactam-resistant P. cepacia CF isolates; the latter isolate was included in a previous study (8). Escherichia coli ATCC 25218, which contains TEM-1 and chromosomal P-lactamases, was used as a control for isoelectric focusing.…”

“…Among 13 CF isolates of P. cepacia, moderate increases in base-line chromosomal ,B-lactamase content far below the levels observed in the derepressed mutant were associated with low-level piperacillin resistance only. Nevertheless, 12 of these strains were resistant to ceftazidime (8). These observations suggest that although derepressed production of chromosomal ,B-lactamase in P. cepacia can mediate high-level P-lactam resistance, this mechanism does not appear frequently in resistant CF isolates of this organism.…”

Effect of pH and CO2 on In Vitro Susceptibility of Pseudomonas cepacia to β-Lactams

“…In particular a 8-lactamase of pI 7.9 was produced by imipenem induction and growth at pH < 7.5. P-Lactamases with pIs in this range in P. ccpacia have been reported but not fully characterized previously (14). Our P-lactamase(s) has the characteristics of a cephalosporinase, and all enzyme activity, regardless of inducing conditions, was inhibitable by clavulanate and tazobactam.…”

“…cepacia has emerged as an important pathogen associated with severe and often fatal infection in children and adults with cystic fibrosis (1, 2, 13). Institution of the most appropriate antimicrobial chemotherapy is of major importance in managing such infections (3,14). Such therapy is often guided by in virro tests of antimicrobial sensitivity.…”

Chloramphenicol resistance in Pseudomonas cepacia because of decreased permeability

“…Isolates from patients with CF, in particular, are often highly resistant to the P-lactam agents and aminoglycosides that are used to treat Pseudomonas aeruginosa (4,9,15). Antibiotics with clinical efficacy against P. cepacia include chloramphenicol, trimethoprim, and the quinolones (12,21,28).…”