[Antimicrobial activity of several drugs against extended-spectrum beta-lactamase positive Enterobacteriaceae isolates in Gifu and Aichi prefecture].

We investigated the antimicrobial activity of several drugs against 131 extended-spectrum beta-lactamase (ESBL) positive clinical isolates in Gifu and Aichi prefecture from 2007 to 2011. Meropenem (MEPM) and doripenem (DRPM) gave the lowest MIC50 at 0.0313 microg/mL. MEPM gave the lowest MIC90 at 0.0625 microg/mL. According to the Clinical and Laboratory Standards Institute breakpoints, the susceptible rates of carbapenems, tazobactam/piperacillin (TAZ/PIPC) and cefmetazole (CMZ) were higher than 90%. The susceptible rates of MEPM, DRPM, imipenem (IPM), TAZ/PIPC and CMZ were 98.5%, 98.5%, 94.7%, 94.7% and 92.4%. We used the PCR method and identified the molecular types of the ESBL positive isolates. Seventy-two strains had CTX-M-9 group gene and CTX-M-9 group gene is the most frequently detected. Against the CTX-M-9 group gene harboring strains which were the most common in our investigation, the susceptible rates of TAZ/PIPC, MEPM, DRPM and IPM were 100%. It is suggested that not only carbapenems but also TAZ/PIPC and CMZ are useful against infections caused by ESBL positive isolates.