High-level β-lactamase activity in sputum samples from cystic fibrosis patients during antipseudomonal treatment

Abstract

The in vivo activity and source of β-lactamase in sputum samples from 43 patients with cystic fibrosis (CF) during a 2-week antipseudomonal treatment were studied. A colorimetric method, based on the conversion of nitrocefin, was used for quantitation of the sputum β-lactamase activity. β-Lactamases in sputum were characterized by isoelectric focusing and inhibition profile and were compared with the β-lactamases extracted from Pseudomonas aeruginosa isolated from the paired sputum samples. We found that the β- lactamase activity increased to high levels in sputum from patients with CF during the course of piperacillin, ceftazidime, cefsulodin, or imipenem therapy. Aztreonam therapy lead to opposite results because the β-lactamase activity decreased and aztreonam was able to mask β-lactamase activity by acting as an inhibitor. All sputum β-lactamases displayed characteristics indicative of a class I enzyme identical to the β-lactamases extracted from P. aeruginosa. The presence of β-lactamase at such levels could lead to in vivo inactivation of β-lactam antibiotics. This study supports the hypothesis that β-lactamase production is an important in vivo resistance mechanism in P. aeruginosa-infected patients with CF.