Antibacterial activity of extracts of leaves of Nerium indicum in combination with antibiotics

Methanol and ethanol extract showed antibacterial activity in range of 0-11 at 10 mg/mL at against all tested bacterial species. Methanol extract with amoxicillin exhibited effective inhibition E. coli. This combination showed antagonistic effect against B. subtilis and S. aureus. Interaction of ethanol extract with amoxicillin also showed effective inhibition against E. coli and decreased activity against B. subtilis and S. aureus. Methanol extract did not show inhibition against P. aeruginosa but it enhanced activity of ciprofloxacin on combination. Ethanol extract also exhibited effective inhibition against P. aeruginosa on combination with ciprofloxacin. But antagonist effect was observed on interaction of both extract with ciprofloxacin against other bacterial species. Interaction of methanol and ceftazidime showed mostly decreased or indifferent effect against all bacterial species. Ethanol extract with ceftazidime resulted in higher inhibition against E. coli. Combination of methanol extract with erythromycin showed higher inhibition against E. coli and also very effective inhibition against S. aureus. This combination resulted in decreased activity against B. subtilis. Ethanol extract with erythromycin also showed synergistic effect against S. aureus and effective inhibition against E. coli. These results indicate that both methanol and ethanol extract has potential to enhance the combination effect with erythromycin against S. aureus and E. coli.