Objectives: Clinical isolates of Klebsiella pneumoniae (91), Escherichia
coli (49), Enterobacter spp. (27), Proteus mirabilis (17), Citrobacter
freundii (2), Providencia stuartii (3) and Serratia spp. (5), with
various MICs of imipenem, were examined for production of
metallo-beta-lactamases (MBLs) with different phenotypic laboratory
tests that have been previously published to detect MBLs in Pseudomonas
aeruginosa and Acinetobacter spp.
Methods: A total of 194 (95 MBL-positive and 99 MBL-negative) clinical
isolates with imipenem MICs <= 0.25 to > 256 mg/L were examined. All
isolates were evaluated by the double-disc synergy test (DDST), the
combination disc test (CDT), the MBL Etest and the modified Hodge test.
The presence of bla(VIM) and bla(IMP) genes was evaluated by in situ
hybridization with specific probes and was certified by PCR.
Results: In 30 bla(VIM)-positive isolates that exhibited MICs of
imipenem <= 4 mg/L, MBL Etest could not be evaluated. CDT with
ceftazidime and 1900 or 750 mu g of EDTA, and DDST after applying an
imipenem disc 10 mm apart from a disc containing similar to 1900 mu g of
EDTA, showed the highest sensitivity (97.9% to 100%) and specificity
(87.9% to 96%) rates among the analysed procedures. CDT with imipenem
and 1900 mu g of EDTA exhibited a sensitivity of 94.7% and showed very
good specificity (98%).
Conclusions: The CDT with imipenem/imipenem+0.5 M EDTA or
ceftazidime/ceftazidime+0.2 M EDTA and the DDST with imipenem 10 mm
apart from EDTA are the most effective methods for the detection of MBLs
in Enterobacteriaceae
