THE COMBINATORIAL EFFECTS OF Azadirachta indica LEAF EXTRACTS WITH AMIKACIN AND TETRACYCLINE AGAINST CLINICALLY IMPORTANT BACTERIA

Antibiotic-resistance is a major threat in the treatment of diseases caused by resistant bacteria. Combination of plant extracts with antibiotics can serve as an alternative to antibiotics. Azadirachta indica (neem plant) has many antimicrobial properties due to the presence of secondary metabolites such as alkaloids and flavonoids. In this study, the combinatorial effects of neem leaf extracts with amikacin and tetracycline against eight clinically important gram-positive and gram-negative pathogens were investigated using the agar well diffusion assay. Synergistic effect of neem leaf extract and tetracycline was observed against Propionibacterium acnes, Bacillus subtilis, and S. pneumoniae  with a significant enlargement (p<0.05) in the diameter of the zone of inhibition. However, the same combination showed insignificant inhibition against S. faecalis, Staphylococcus epidermidis, Enterococcus faecalis, and Staphylococcus aureus. The neem leaf extract-amikacin combination showed insignificant antibacterial activity against Staphylococcus aureus, S. epidermidis, S. pneumoniae, and Pseudomonas aeruginosa. An antagonistic effect was observed when Bacillus subtilis was exposed to the same combination as there was a significant reduction (p<0.05) in the zone of inhibition.  This study suggests the potential development of the neem leaf extract-tetracycline combination as an antibacterial agent against P. acnes, B. subtilis, and S. pneumoniae. However, this preliminary data requires further investigation and test on a wider range of clinical isolates to make a more decisive conclusion. The antagonistic effect of the neem leaf extract and amikacin suggests that the individual agents are potent as antibacterial agents than the combination