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

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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 ≈ E age > E amp . In contrast, S. aureus incubated with low ampicillin (≤50µg 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 ≈ E age ≈ E amp . CONCLUSION: The trend E native ≈ 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.