Metallo-β-lactamase-producing Enterobacteriaceae isolates in a university hospital in Taiwan: Prevalence of IMP-8 in Enterobacter cloacae and first identification of VIM-2 in Citrobacter freundii

A total of 9082 clinical isolates of Enterobacteriaceae other than Klebsiella spp. collected in 1999 and 2000 at a university hospital in Taiwan were investigated for the production of metallo-β-lactamases (MBLs). Thirty-six (2.9%) of the 1261 Enterobacter cloacae isolates and one (0.3%) of the 340 Citrobacter freundii isolates were found to carry bla_IMP-8 and bla_VIM-2, respectively, by colony hybridization, PCR and sequence analysis. The IMP-8 producers were recovered from 20 patients and four of them had recently transferred from other hospitals, implying spread of IMP-8-producing E. cloacae among different healthcare settings. Of the 20 non-repetitive IMP-8 producers, 17 (85%) isolates also harboured bla_SHV-12, which was on the same transferable plasmids with bla_IMP-8. The bla_VIM-2-positive isolate and all non-repetitive bla_IMP-8-positive isolates appeared susceptible to imipenem (MICs < 8 mg/L) and meropenem (MICs < 4 mg/L), indicating the difficulty in detection of MBLs in Enterobacteriaceae by routine susceptibility testing. Ribotyping of the IMP-8-producing E. cloacae isolates indicated that the dissemination of bla_IMP-8 was due largely to the spread of an epidemic clone, but horizontal transfer among unrelated strains also occurred.