Assessment of combined antimicrobial activity of Azadirachta indica herbal leaf preparation and selected antibiotics against a clinical isolate of Escherichia coli: A susceptibility pattern analysis

Abstract

The aim of this study is to investigate the in vitro antimicrobial interaction between Azadirachta indica crude water extract and standard antibiotics (tetracycline, doxycycline, ampicillin, cefuroxime, streptomycin, gentamicin, ciprofloxacin, norfloxacin, and erythromycin). In vitro interactions were evaluated via agar diffusion and Checkerboard techniques against E. coli as the test microorganism. Synergistic interactions were observed between crude extract (0.1 mg/ml or 0.25 mg/ml) and all antibiotics used (p < 0.05). Checkerboard technique revealed fractional inhibitory concentration (FIC) index indicating synergy with tetracycline (1:9). Co-administration of tetracycline, doxycycline, gentamicin, streptomycin, erythromycin, cefuroxime, ciprofloxacin, or norfloxacin with A. indica crude extract may offer clinical benefits in treating E. coli infections.