Novel combinations of antibiotics to inhibit extended-spectrum β-lactamase and metallo-β-lactamase producers in vitro: a synergistic approach

Abstract

Aim: To determine the synergistic effect of different antibiotics, alone and in combination, against extended-spectrum β-lactamase and metallo-β-lactamase producers. Materials & methods: MIC values of different antibiotics were determined for a total of 12 strains, of which nine strains were of clinical origin and the remainder were reference strains. In vitro synergy testing was performed for all the isolates using microdilution, chequerboard techniques and time-kill assays. Results: Out of the all the combinations, cefoxitin gave the highest rate of synergy by pairing up with streptomycin and cefotaxime to form effective combinations against multidrug-resistant strains of bacteria. However, the combination of cefotaxime and cefoxitin showed synergistic activity against both NDM-1-producing strains. Conclusion: Novel synergistic combinations were observed against different resistant strains, including NDM-1 producers.