Antibiotics have been widely used in the livestock industry for prophylaxis, treatment, and as growth promoters, for over sixty years. This extensive use of antibiotics has applied a selection pressure on bacteria, leading to high levels of antibiotic resistance. This has led to a decreased efficacy of the drugs in animal health, and also human health through zoonotic transfer. In order to reduce the pressure on currently used antibiotics, and the risk of mortality from common bacterial infectious diseases, novel antimicrobials need to be found; although this process has been very slow. Many new formulations found require extensive pharmaceutical testing, and often do not succeed due to lack of efficacy. In traditional medicine, plants such as garlic, have shown antimicrobial activity. Garlic (Allium sativum) is said to have a broad-spectrum of activity against both Grampositive and Gram-negative bacteria, and thus could be a potential benefit for the cattle and sheep industry by reducing antimicrobial resistance and consequently costs. This study involved a comparison of the effectiveness of different preparations of garlic, with two commonly used antibiotics in the farming industry: ampicillin and tetracycline, on commonly isolated gut bacteria. Nutrient agar infusions and the Kirby-Bauer disc diffusion assay were used to determine the susceptibility of bacteria in the faeces of cattle and sheep to garlic, ampicillin and tetracycline. The comparison found that tetracycline was the most effective antimicrobial in inhibiting bacterial growth, with garlic exerting a mild antibiotic effect on most livestock bacterial isolates. This mild efficacy suggests that perhaps garlic could potentially be used as a prophylactic in the livestock industry to reduce the pressure on conventional antimicrobial agents.
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