COMPARATIVE ACTIVITY OF PIPERACILLIN TAZOBACTAM AGAINST CLINICAL ISOLATES OF EXTENDED-SPECTRUM BETA-LACTAMASE-PRODUCING ENTEROBACTERIACEAE/

beta-Lactam resistance on the part of the Enterobacteriaceae causes se rious therapeutic problems in our institutions due to their production of extended-spectrum beta-lactamases (ES beta Ls). We studied the in vitro activity of beta-lactam/beta-lactamase inhibitor combinations an d third-generation cephalosporins and monobactams against 71 clinicall y relevant Enterobacteriaceae which produced TEM- and SHV-derivative E S beta Ls. Of the single drugs and combinations tested, piperacillin/t azobactam proved to be the most effective. Piperacillin/tazobactam was highly active against Proteus mirabilis, with minimum inhibitory conc entrations (MICs) ranging from 0.125 to 16 mu g/ml; Escherichia coli ( MICs from 2 to 16 mu g/ml) and Serratia marcescens (MICs from 4 to 8 m u g/ml), while its activity against Klebsiella pneumoniae ES beta L pr oducers turned out to be closely related to the type and the amount of enzyme produced, the MIC ranging from 1 to 128 mu g/ml. The antibacte rial activity of piperacillin/tazobactam was stronger than that of tic arcillin/clavulanate, ceftriaxone, cefotaxime, ceftazidime and aztreon am, and the combination shared favorable in vitro activity properties against the ES beta L producers with imipenem which, however, should b e kept as reserve product.