In Vitro Efficacy of Biocompatible Zinc Ion Chelating Molecules as Metallo-β-Lactamase Inhibitor among NDM Producing...

Objective  This article assesses the effectiveness of captopril, tetracycline, and ciprofloxacin as metallo-β-lactamase (MBL) inhibitors against New Delhi metallo-β-lactamase (NDM)-producing Escherichia coli. Materials and Methods  Twenty-four well-characterized carbapenem-resistant E. coli isolates which produced NDM ( n  = 21) and Oxa-48-like enzymes ( n  = 3) were used to assess the inhibitors. The positive control organism was designed by cloning the NDM gene into pET-24a plasmid and transforming it into expression vector E. coli BL21. All the proposed inhibitors were assessed for their interaction with MBLs using checkerboard minimum inhibitory concentration (MIC) assay with imipenem and meropenem. The fractional inhibitory concentration (FIC) index was calculated to assess the activity of molecules. Results  The E. coli BL21 (DE3) pET-24a- bla _NDM showed carbapenem resistance upon isopropyl β-D-1-thiogalactopyranoside induction and had MIC of 32 µg/mL for both imipenem and meropenem. For the test isolates, ∑FIC values of imipenem and meropenem with ethylenediaminetetraacetic acid (EDTA) ranged from 0.039 to 0.266 and 0.023 to 0.156, respectively. At a 256 µg/mL concentration, captopril had ∑FIC index value for imipenem and meropenem as 0.133 to 0.375 and 0.133 to 0.188, respectively. The tetracycline and ciprofloxacin in combination with meropenem/imipenem showed indifferent results. Conclusion  Among the three molecules tested, captopril had MBL inhibitory activity, but the concentration required for inhibition was beyond the therapeutic safety levels. Ciprofloxacin and tetracycline had weak or no MBL inhibitory activity. Checkerboard MIC of EDTA with carbapenem antibiotic and control organism with NDM enzyme production helped us create a reference system for comparing and assessing the results of potential MBL inhibitors in future.