Antibiofilm and synergistic antibacterial effect of Garlic (Allium sativum) against Methicillin resistant Staphylococcus aureus (MRSA)

Abstract

Background: Methicillin resistant Staphylococcus aureus (MRSA) is one of main bacterial pathogens that is associated with difficult to treat nosocomial and community infections with high mortality. Shiga toxin producing E. Coli (STEC) infections result in bloody diarrhea, vomiting and mild fever. Biofilm formation has been linked with pathogenicity and virulence of these bacterial pathogens. Garlic (Allium sativum) has been traditionally used as an antibacterial agent in India and South East Asia. We have demonstrated that garlic exhibits antibiofilm and antibacterial activity against drug resistant STEC clinical isolates. In addition, organosulphide compounds of garlic have been reported to exhibit antibacterial activity against MRSA. In view of these observations, our laboratory wanted to investigate if crude garlic extract has any antibiofilm activity against MRSA. Further, we wanted to test if for synergistic effect of garlic when used in combination with antibiotics. Methods and materials: The study was performed with three MRSA isolates. Standard disc diffusion, serial dilution and kill curve assays were performed to access the antibacterial and synergistic activity of garlic against MRSA. In vitro microtiter plate assay was performed to quantify the formation of biofilm in the presence and absence of garlic crude extract. In addition, the effect of garlic on biofilm formation was also evaluated using scanning electron microscopy (SEM). Results: The results indicated that crude garlic extract exhibited significant dose dependent antibacterial activity against MRSA and the activity was much better in terms of clarity of zones of inhibition compared to pure organosulphide compounds found in garlic. It was interesting to note that sub-MIC concentrations of garlic were able to sensitize MRSA to methicillin. Garlic at sub-MIC concentrations reduced MRSA biofilm formation by more than 60%. We conclude that crude garlic extract has more antibacterial activity than its active ingredients. This is the first study to report its antibiofilm property against MRSA to best of our knowledge. Conclusion: Garlic organosulphide compounds have the potential to be used in combination with standard antibiotics to treat drug resistant bacterial infections. Garlic organosulphide compounds based novel antibiotic and antibiofilm drugs can be developed to tackle the problem of antibacterial drug resistance.