Atomic force microscopy study of the antimicrobial activity of aqueous garlic versus ampicillin against Escherichia coli and Staphylococcus aureus

BACKGROUND: In this study the effects of ampicillin and aqueous garlic extract on Escherichia coli (ATCC 9637) and Staphylococcus aureus (ATCC 25923) were compared. Atomic force microscopy (AFM) was used to study the possible mechanisms of membrane disruption. RESULTS: Ampicillin disrupted the cell membrane of E. coli, inducing pores and cell leakage. Aqueous garlic extract also induced leakage from the cell membrane in E. coli, but no pores were observed. The trend in Young's modulus for E. coli was E-native approximate to E-age > E-amp. In contrast, S. aureus incubated with low ampicillin (<= 50 mu g mL(-1)) and garlic (<= 50 mg mL(-1)) concentrations showed no significant changes in surface morphology compared with the untreated bacterium. The trend in Young's modulus for S. aureus was E-native approximate to E-age approximate to E-amp. CONCLUSION: The trend E-native approximate to E-age for E. coli and S. aureus supports the hypothesis that the compounds in garlic show intracellular activity. This proof-of-concept study of the aqueous crude isolate of garlic points to the feasibility of further AFM investigations to compare the antimicrobial properties of various pure thiosulfinate isolates found in garlic. (c) 2009 Society of Chemical Industry