# 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

## TL;DR

This study tested garlic, ginger, and onion extracts to see if they can inhibit bacteria causing mastitis in dairy cows, finding that only garlic showed antibacterial effects.

## Contribution

The study demonstrates that garlic extract has in vitro antibacterial activity against E. coli and S. aureus from mastitis-affected cows.

## Key findings

- Garlic extract inhibited E. coli and S. aureus at minimum inhibitory concentrations of 1.56 µL/mL and 3.12 µL/mL, respectively.
- Minimum bactericidal concentrations of garlic were 12.5 µL/mL for E. coli and 25 µL/mL for S. aureus.
- Ginger and onion extracts showed no inhibitory activity at tested concentrations.

## Abstract

Bovine mastitis is a common disease in dairy cows that is often treated with antibiotics, but there is increasing concern that use of antibiotics on farms may contribute to the development and spread of resistant bacteria. Identification of non-traditional treatments may help to reduce potential development of antimicrobial resistance. The purpose of this study was to determine if extracts of garlic, ginger, and onion were able to inhibit growth of E. coli and S. aureus that had been isolated from milk samples of cows with mastitis. Fresh extracts of garlic, ginger, and onion were tested in vitro across a range of concentrations. Garlic inhibited growth of both organisms, but extracts of fresh ginger and onion were not able to inhibit growth. Future studies are needed to determine if garlic can reach an effective concentration in the mammary gland and efficacy in naturally occurring infections.

The purpose of this study was to identify the potential inhibitory effects of extracts of garlic, ginger, and onion on Escherichia coli and Staphylococcus aureus, 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 E. coli ATCC 25922 and S. aureus 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 E. coli and S. aureus, respectively. The minimum bactericidal concentrations of garlic extract against E. coli and S. aureus 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 E. coli and S. aureus. 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.