[In vitro activity of piperacillin-tazobactam against Klebsiella pneumoniae clinical isolates, producers or not of extended spectrum beta-lactamases].

The aim of this study was to determine the in vitro activity of piperacillin-tazobactam against 81 clinical isolates of Klebsiella pneumoniae. The clinical specimens were processed according to standard microbiological procedures and 81 K. pneumoniae isolates were identified using MicroScan Panels following the manufacturer's recommendations. A double disk diffusion method was applied to detect extended spectrum betalactamases (ESBL) (43 isolates were positive and 38 were negative). Minimum inhibitory concentrations (MIC) were determined by an agar dilution technique using Mueller-Hinton. The following antibiotics were studied: piperacillin with 4 mg/l of tazobactam, amoxicillin-clavulanic acid in a 2:1 proportion, cefotaxime, ceftriaxone, cefepime, imipenem and meropenem. The MIC(90) were 16/4 mg/l for piperacillin-tazobactam, 16/8 for amoxicillin-clavulanic acid, 16 for ceftriaxone, 16 for cefotaxime, 4 for cefepime, 0.25 for imipenem and 0.032 for meropenem in ESBL-positive strains. In ESBL-negative strains the MIC90 were as follows: 4/4 mg/l for piperacillin-tazobactam, 8/4 for amoxicillin-clavulanic acid, 0.064 for ceftriaxone, 0.125 for cefotaxime, 0.125 for cefepime, 0.125 for imipenem and 0.016 for meropenem. All betalactams showed excellent in vitro activity against ESBL non-producer K. pneumoniae. Moreover, piperacillin-tazobactam and both carbapenems showed good in vitro activity against EBSL-producer K. pneumoniae.