Relationship between β-lactamase production and resistance phenotype in Klebsiella pneumoniae strains.

This study was designed to evaluate the resistance phenotypes of β-lactamases-producing Klebsiella pneumoniae strains. The antibiotic susceptibility and β-lactamase activity of K. pneumoniae strains, including antibiotic-sensitive K. pneumoniae (KPWT), ciprofloxacin-induced resistant K. pneumoniae (KPCIP) and clinically isolated K. pneumoniae strains (KPCI237, KPCI263 and KPCI272) were determined in the absence and presence of β-lactamase inhibitors (BLI 489, sulbactam, clavulanate and tazobactam). All strains were highly resistant to ampicillin in the absence of β-lactamase inhibitors (MIC≥ 512 μg mL-1). In the presence of clavulanate, the MICs of ampicillin and piperacillin against KPWT were decreased by > 64-fold and 4-fold, respectively. The resistance of KPCI263 to cefotaxime, ceftazidime, ceftriaxone and piperacillin were increased in the presence of BLI-489. The antibiotic susceptibility of KPCI237 to β-lactams was not noticeably changed in the presence of β-lactamase inhibitor (clavulanate, sulbactam or tazobactam). KPWT, KPCIP and KPCI272 were positive for blaSHV, blaAmpC and blaFOX/MOX; KPCI237 for blaSHV and blaAmpC; and KPCI263 for blaSHV and blaOXA-48. The antibiotic susceptibility corresponded well with the results obtained from dual disc diffusion assay, which was in good agreement with the β-lactamase production. The results provide useful information for understanding the resistance phenotypes in association with β-lactamase production.