Comparative in vitro activity of piperacillin/tazobactam against gram-negative bacilli

To describe the in vitro activity of piperacillin/tazobactam against clinical isolates of Gram-negative bacteria, compared with other antibacterial agents.

Survey of susceptibility of clinical isolates of Gram-negative bacilli.

Academic hospitals of the University isolates of the Witwatersrand teaching complex. BACTERIAL STRAINS: 180 selected clinical isolates of Gram-negative bacilli.

Minimum inhibitory concentrations (MICs) determined by agar dilution using techniques according to the recommendations of the National Committee for Clinical Laboratory Standards.

Ciprofloxacin, biapenerm, imipenem, cefepime and cefpirome were all highly active against most of the Enterobacteriaceae. All the ampicillin-resistant strains of Enterobacteriaceae were susceptible to piperacillin/tazobactam, MIC90 values being 4/4 mg/l for Klebsiella and Proteus/Providencia spp., 8/4 mg/l for Citrobacter and Serratia spp., and 16/4 mg/l for Escherichia coli. All the agents, with the exception of ampicillin (MIC90 4 mg/l) and chloramphenicol (MIC90 4 mg/l), were highly active against the Haemophilus influenzae isolates tested. All Bacteroides fragilis strains were susceptible to piperacillin/tazobactam (MIC90 8/4 mg/l), as well as to co-amoxiclav (MIC90 4/2 mg/l), biapenem and imipenem (MIC90s 0.5 mg/l). The Pseudomonas spp. tested included strains resistant to piperacillin/tazobactam, ceftazidime, biapenem, gentamicin, tobramycin and ciprofloxacin. Cefepime was the most active agent against Pseudomonas isolates, with 90% of the strains being susceptible to this agent, while biapenem was the most active agent against the Acinetobacter isolates investigated.

The in vitro spectrum of activity of piperacillin/tazobactam against the majority of isolates was comparable to those of the other new agents tested.