Syzigium cumini and Mangifera indica Seed Extracts: In Vitro Assessment for Antibacterial Activity Alone and in Combination with Antibiotics against Clinical Bacteria

Objective: To determine the antibacterial activity of Syzigium cumini (Family: Myrtaceae) and Mangifera indica (Family: Anacardiaeceae) seed extracts, alone and in combination with some conventionally used antibiotics, against clinical isolates of Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus. Method: The antibacterial activity of ethanolic S. cumini seed extract (SSE) and M. indica seed extract (MSE), at different concentrations, were determined by disk diffusion. The combined activity with antibiotics of the extracts (SSE and MSE) was determined against the test isolates. The ZDI (zone diameter of inhibition) values for the agents (alone and in combination) were recorded, and growth inhibitory indices (GIIs) were calculated. Result: The bacterial isolates were multidrug resistant, against which the SSE and MSE had excellent activity; ZDIs of SSE and MSE for E. coli and K. Pneumoniae ranged 8 20 mm, whereas for Staph. aureus ZDIs were 8 18 mm. The extracts (SSE and MSE) in combination with trimethoprim and vancomycin showed synergistic effect against all the test bacteria (GIIS: 0.53–1.0). The extracts, combined with ampicillin, ciprofloxacin and methicillin, had mixed interaction: synergistic (GIIs: 0.53–1.0) as well as antagonistic (GIIs: 0.37–0.47) against the test strains. Conclusion: The plant extracts (SSE and MSE), having broad antibacterial activity alone, and synergistic interaction in combination with antibiotics against the human pathogenic bacteria, might be useful in preparing nonantibiotic as well as combined treatment regimen against bacterial infection to humans.