In vitro activities of various piperacillin and sulbactam combinations against bacterial pathogens isolated from Intensive Care Units in Taiwan:SMART 2004 programme data

We investigated the in vitro activity of various piperacillin and sulbactam combinations against Gram-negative bacterial isolates from
Intensive Care Units (ICUs) in Taiwan. Antimicrobial susceptibility testing of 1030 bacterial isolates recovered from ICUs of nine major
teaching hospitals was performed using the agar dilution method. Sulbactam was added to piperacillin either at a fixed sulbactam concentration
of 4 mg/L and 8 mg/L or at a piperacillin:sulbactam ratio of 2:1 and 4:1. Piperacillin/sulbactam at a ratio of 2:1 or a fixed 8 mg/L concentration
of sulbactam had better activities against Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis and Serratia marcescens than other
piperacillin/sulbactam formulations. For Pseudomonas aeruginosa, piperacillin/sulbactam (2:1 or 4:1 ratios) had MIC90 values (minimum
inhibitory concentration for 90% of the organisms) of 64 mg/L (>90% susceptibility) compared with 64 mg/L for cefoperazone/sulbactam
(68% susceptibility) and 128 mg/L for piperacillin/tazobactam (82% susceptibility). For Acinetobacter baumannii, both piperacillin/sulbactam
(either 2:1 ratio or a fixed 8 mg/L sulbactam) and cefoperazone/sulbactam were the most potent agents. Adding sulbactam to piperacillin resulted
in increased susceptibility rates among piperacillin-resistant P. aeruginosa (53–57% in either 2:1 or 4:1 ratios) and A. baumannii (38–46% in
either 2:1 ratio or a fixed 8 mg/L concentration of sulbactam) isolates. Results of susceptibility tests with piperacillin/sulbactam are dependent
on the method used. Piperacillin/sulbactam combinations possessed better in vitro activities than piperacillin alone or piperacillin/tazobactam
against P. aeruginosa and A. baumannii.
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