Susceptibility Pattern of a Clinical Isolate of Staphylococcus aureus to the Combined Activity of a Herbal Preparation of Azadirachta indica and Some Antibiotics

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Purpose: To investigated the in vitro antimicrobial interaction between the crude water extract of Azadirachta indica and some standard antibiotics; doxycycline, gentamicin, streptomycin, erythromycin, ciprofloxacin, and norfloxacin. Methods: The in vitro interactions were evaluated using a combination of agar diffusion and Checkerboard techniques against Staphylococcus aureus as test microorganism. Results: There were synergistic interactions between the crude extract (0.1 mg/ml or 0.25mg/ml extract) and all the antibiotics used except tetracycline in the agar diffusion technique (p< 0.05). In the Checkerboard technique, fractional inhibitory concentration (FIC) index reveal that the crude extract were synergistic with either tetracycline (1:9), streptomycin (1:9, 9:1), ciprofloxacin (2:8, 5:5) or norfloxacin (2:8, 6:4). Conclusion: There is a possible beneficial clinical application of the co-administration of doxycycline, gentamicin, streptomycin, erythromycin, ciprofloxacin or norfloxacin and the crude extract of A. indica in the treatment of infections caused by S. aureus. However, unguided concomitant usage may result in therapeutic failure. Keywords: Staphylococcus aureus, interaction, antibiotics, FIC index