Antibacterial potential of Azadirachta indica seed and Bacopa monniera leaf extracts against multidrug resistant Salmonella enterica serovar Typhi isolates

Introduction: Neem (Azadirachta indica) and brahmi (Bacopa monniera) are well known medicinal plants, but their antibacterial activity against the typhoidal pathogen Salmonella enterica serovar Typhi has not been studied. Material and methods: A. indica seed and B. monniera leaf extracts were assayed for antibacterial activity by agar well diffusion and agar dilution methods in order to determine the zone diameter of inhibition and minimum inhibitory concentration (MIC) values, respectively. Killing efficacy of the extracts was determined at various concentrations in Mueller-Hinton broth. Time-dependent killing was achieved using 500 μg/ml (1× MIC) of the extract for S. enterica serovar Typhi strain. Results: The A. indica seed and B. monniera leaf extracts showed excellent antibacterial activity against the isolates having zone diameter of inhibition 9-19 mm and 9-18 mm. The MICs for the isolates were in the range 50-500 μg/ml (A. indica extract) and 50-600 μg/ml (B. monniera extract). The A. indica and B. monniera extracts were bactericidal against S. enterica serovar Typhi at concentrations of 400 μg/ml and 450 μg/ml, respectively. A. indica and B. monniera against the test microorganisms displayed significant antibacterial (at concentrations ≥250 and 300 μg/ml, respectively) as well as time killing (at 500 μg/ml) activities (p<0.005). Conclusions: The results might explain the ethnobotanical use of the studied plants for the treatment of S. enterica serovar Typhi infection. This is the first evaluation of A. indica and B. monniera against S. enterica serovar Typhi isolates associated with enteric fever in and around Kolkata (India) in the past one and half decade.