Antimicrobial activity of tazobactam/piperacillin against clinical isolates from 2001 to 2006 in Japan

Antimicrobial susceptibility to beta-lactam antibiotics including tazobactam/piperacillin and beta-lactamases production were evaluated for 3,213 clinical isolates of 11 strains, 2 spp., and 1 group obtained from 12 hospitals from 2001 to 2006 in Japan. Susceptibility to tazobactam/piperacillin calculated based on Clinical and Laboratory Standards Institute breakpoints were 59.2%-100%. Tazobactam/piperacillin showed up to 90% susceptibility of 8 strains, 1 sp., and 1 group. Chronological MIC increase of tazobactam/ piperacillin was not seen in any species. Isolation frequency of beta-lactamases producing strains increased in Escherichia coli and Serratia marcescens from 68.1% to 97.3% and from 81.0% to 96.2%. Isolation frequency of metallo beta-lactamase(MBL) producing strains increased in Pseudomonas aeruginosa from 5.8% to 8.6%, and those of extended-spectrum beta-lactamases (ESBLs) producing strains also increased in E. coli, Klebsiella pneumoniae and Proteus mirabilis from 1.8% to 6.4%, from 1.1% to 4.7% and from 1.6% to 9.2%. Antimicrobial activity of tazobactam/piperacillin against MBL producing strains was superior to other beta-lactam antibiotics, as were those against ESBLs producing strains for other beta-lactam antibiotics other than flomoxef. Results for tazobactam/piperacillin susceptibility of clinical strains isolated in Japan from 2001 to 2006 showed that tazobactam/piperacillin maintained sufficient antibacterial activity against these strains, including beta-lactamase producing strains, although the isolation frequency of MBL and ESBLs producing strains increased.