Antimicrobial Effects of Garlic Extracts against Multidrug Resistant Staphylococcus aureus Isolates from Clinical Specimens

Aim: To assess the antibacterial potentials of Allium sativum and their interaction with antibiotics against clinical isolates of multidrug resistant Staphylococcus aureus.

Study Design: The study is designed to investigate the antibacterial activity of Allium sativum extract and its interactive potential to enhance the activity of antibiotics against multidrug resistant S. aureus.

Place and Duration of Study: The study was conducted between May, 2015 and June, 2016. This study was performed at the Microbiology laboratory of the Akanu Ibiam Federal Polytechnic, Unwana, Ebonyi State, Nigeria.

Methodology: Extraction was done using sterile water, acetone and methanol. The extracts were evaporated to dryness using rotary evaporator. Antibacterial susceptibility testing was carried out using the agar well diffusion method. The macrobroth dilution method was used to determine the MIC of the methanol extracts. Checkerboard method was used to determine the interaction between extracts and antibiotics.

Results: Aqueous and methanol extracts of Allium sativum had inhibition zone range of 10 ± 1.50 to 17 ± 1.50 mm and 7 ± 1.05 to 14 ± 0.95 mm respectively, at concentration range of 25 to 200 mg/ml. Acetone extract had inhibition range of 5 ± 0.50 to 11 ± 0.50 mm. Methanol and acetone extracts had the same inhibition zone (14 ± 0.79 mm) diameter against the S. aureus isolates at 200 mg/ml. There were no significant difference found between inhibition zone diameter of methanol/acetone extract (P = 0.50), methanol/aqueous extracts (P = 0.97) and acetone/aqueous extracts (P =0.48) against the test bacteria. The correlation analysis done between inhibition zone diameter and concentration of A. sativum recorded a positive correlation (r) ranging between 0.84 and 0.89. The combination of methanol extracts of garlic (MEG) plus ceftazidime (Caz) and MEG plus erythromycin (Ery) showed synergistic interaction in three and four of the isolates respectively. Antagonistic interaction was recorded in the combination of MEG plus cefuroxime in one isolate whereas it was recorded in three isolates in the interaction of MEG and ciprofloxacin. The synergistic interaction stood at 28.0% and antagonism 16.0%. The combination of ½ x MIC of MEG plus ½ x MIC Caz against S. aureus showed bactericidal activity against the isolates at 12 hours resulting in a 4.25 log10 cfu/ml reduction whereas the combinations of ½ x MIC of MEG plus ½ x MIC of Ery showed bactericidal activity after 8 hours with a 3.13 log10 cfu/ml decrease. The net reduction in colony counts was observed consistently between 12 – 24 hours.

Conclusion: The result of this study showed that methanol extract of A. sativum possesses bactericidal activities against S. aureus. In addition, the methanol extract may be a potential source of resistance modifying compounds that can potentially improve the performance of antibiotics in the treatment of multidrug resistant S. aureus infections. There is need to isolate the specific active agent(s) involved in the potentiation for drug compounding.