THE INVITRO ACTIVITY OF PIPERACILLIN TAZOBACTAM, CIPROFLOXACIN, CEFTAZIDIME AND IMIPENEM AGAINST MULTIPLE RESISTANT GRAM-NEGATIVE BACTERIA

One hundred and fifty Gram-negative bacterial strains including respiratory pathogens, such as Haemophilus influenzae and Branhamella catarrhalis, and Enterobacteriaceac with known resistance to β-lactam and other antibiotics were tested in vitro for sensitivity to piperacillin, piperacillin/tazobactam (ratio 8:1), ceftazidime, ciprofloxacin and imipenem. A 16-fold or greater reduction in the MIC90, of piperacillin was achieved by the addition of tazobactam, in the respiratory pathogens, thus bringing them within the susceptible range. Among the Enterobacteriaceae, a 32-fold or greater reduction in the MIC90 was found for Providencia stuartii, Proteus mirabilis and Aeromonas hydrophila. When compared with the other three antimicrobials, the combination was found to be active against fewer species of multiply resistant Enterobacteriaceae, but equally effective against H. influenzae and B. catarrhalis. © 1990 The British Society for Antimicrobial Chemotherapy.