Single and joint antibacterial activity of aqueous garlic extract and Manuka honey on extended-spectrum beta-lactamase-producing Escherichia coli.

Background: Multidrug resistance and recent technological advances have renewed interest in natural product drug discovery from ancient remedies such as Allium sativum (garlic) and honey. This study assessed antibacterial activity of aqueous garlic extract (AGE) and Manuka honey on extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli.

Methods: Thirty clinical isolates of E. coli were collected and screened for ESBL production by double-disc synergy test. Single and joint antibacterial activity of AGE and Manuka honey against ESBL-producing E. coli were determined by agar well dilution and checkerboard methods, respectively.

Results: Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of AGE ranged from 125-250 mg/mL and 250-500 mg/mL, respectively. MIC and MBC of Manuka honey ranged from 12.5-25% v/v and 25-50% v/v, respectively. The combination of AGE and Manuka honey exhibited different effects on selected ESBL-producing E. coli; synergism (1/4H+1/16G), additive (1/8H+1/2G, 1/2H+1/16G), indifference (1/16H+MICG, MICH+1/16G, 2MICH+1/32G) and antagonism (4MICH+1/32G).

Conclusions: Manuka honey exhibited greater antibacterial activity against ESBL-producing E. coli than AGE. Antibacterial activity, and the interaction of AGE and Manuka honey against ESBL-producing E. coli are dependent on their concentration. Studies assessing antibacterial activity of potent phytochemicals in AGE and honey would provide insights to mechanisms of interaction for development of new drug leads.