[Successful isolation of IMP-1 carbapenemase-producing, but not carbapenem-resistant species in Enterobacteriaceae family].

Carbapenemases including Klebsiella pneumoniae carbapenemases (KPC) are widespread among clinical isolates in the family Enterobacteriaceae. In 2008, we isolated 4 IMP-1 metallo-beta-lactamase (MBL) producers of this family having transferable carbapenem-resistance markers. When examined with MicroScan Neg-Combo Panels, all 4 showed imipenem-MIC of either <1 microg/mL or 2 microg/mL, although they were highly resistant to ceftazidime (MIC: >16 microg/mL). When isolates were examined by Sensi-Disc, however, discrepancies were seen in susceptibility testing results against carbapenems, i.e., some strains were susceptible to imipenem but resistant to meropenem. MBL productivity of isolates could be ensured by both sodium mercaptoacetic acid (SMA) and modified Hodge testing. Noted that atypical carbapenemase-producers may be overlooked in routine clinical microbiology laboratory testing, and both SMA disks and modified Hodge tests proved appropriate for accurately detecting such carbapenemase-producers.