Evaluation of In Vitro Inhibitory Activity of Extracts of Garlic, Ginger, and Onion Against Escherichia coli and Staphylococcus aureus Isolated from Milk of Dairy Cows

The purpose of this study was to identify the potential inhibitory effects of extracts of garlic, ginger, and onion on <i>Escherichia coli</i> and <i>Staphylococcus aureus</i>, which had been previously isolated from milk of dairy cows with mastitis. Garlic, ginger, and onions were crudely pressed, and the extracts were filtered and tested for their ability to inhibit bacterial growth at a wide range of concentrations, from undiluted to 1:512 (2^-9). Their inhibitory properties were compared to positive controls containing ampicillin and ceftiofur, and negative controls containing only the nutrient medium and bacteria. Each plate contained quality control organisms <i>E. coli</i> ATCC 25922 and <i>S. aureus</i> ATCC 25923. The colorimetric microdilution method with resazurin as an indicator of bacterial growth was used to determine the minimum inhibitory concentrations. In addition, the minimum bactericidal concentrations of the extracts were assessed. The minimum inhibitory concentrations of garlic extracts were 1.56 µL/mL and 3.12 µL/mL for <i>E. coli</i> and <i>S. aureus</i>, respectively. The minimum bactericidal concentrations of garlic extract against <i>E. coli</i> and <i>S. aureus</i> were 12.5 and 25 µL/mL, respectively. For both ginger and onion, no inhibition was detected at the full concentration of the extracts, but garlic extract demonstrated in vitro inhibition against both <i>E. coli</i> and <i>S. aureus</i>. Future studies should evaluate the ability of garlic extracts to achieve an inhibitory concentration in milk and explore its potential activity in naturally infected mammary glands.