Metallo-β-lactamase-producing Enterobacteriaceae isolates at a Taiwanese hospital: Lack of distinctive phenotypes for screening

We investigated the prevalence of metallo-β-lactamases (MBLs) among 1,827 Enterobacteriaceae isolates collected in 2006 and evaluated the VITEK 2 microbiology system, modified Hodge test, and 2 combined disk tests as the screening tools for MBLs by using these isolates and 77 previously characterized IMP-8 producers. The IMP-8 MBL was identified in 18 isolates of 2006, and the IMP-8-positive isolates represented 0.2%, 1.1%, and 5.0% of all Escherichia coli, Klebsiella pneumoniae, and Enterobacter cloacae isolates, respectively. Only one-third of all MBL producers could be recognized by either VITEK 2 or the Hodge test. MBL production could be identified in 38 (40%) of the 95 IMP-8-producing isolates by the combined disk test using meropenem disks supplemented by phenylboronic acid and EDTA, and only 2 (2.1%) isolates gave positive results in the combined disk test using meropenem disks supplemented with dipicolinic acid. Of all IMP-8 producers, 37.9%, 50.5%, and 32.6% were nonsusceptible to tigecycline, fluoroquinolones, and both, respectively. In conclusion, this study demonstrated the lack of distinct phenotypes that could be easily identified among the IMP-8-producing Enterobacteriaceae isolates at a Taiwanese hospital. Continuous surveillance and monitoring are needed because the widespread of tigecycline- and fluoroquinolone-coresistant MBL producers may become a serious therapeutic problem.