Antimicrobial Activities of Plant Extracts Against Bacteria Associated with Bovine Mastitis

Bovine mastitis is mainly caused by bacterial infection of cow's udders, resulting in milk of lower quality. Antibiotic treatment of mastitis can leave antibiotic residues in milk and can increase antibiotic resistant bacteria in the food chain. The aims of this study were to investigate antimicrobial activities of selected natural extracts from traditional Thai plants against bovine mastitis-associated bacteria, in order to evaluate the possibility of using plant extracts as alternatives to antibiotics for bovine mastitis treatment and control. Rhizome and leaf plants (two types for each category) were chosen in this study, including Curcuma mangga (Mango ginger), Zingiber montanum (J. Koenig) Link ex A. Dietr. (Cassumunar ginger), Azadirachta indica A. Juss (Neem leaf) and Piper betle Linn. (Betel Pepper leaf). Antimicrobial activities of the aqueous and 70% ethanolic extracts of these plants were determined against 12 species of bovine mastitis-associated genera: Staphylococcus and Streptococcus, using disc diffusion, MIC and MBC assays. Extracts from P. betle and C. mangga showed inhibitory effects against the mastitis-associated bacterial isolates/strains tested. The 70% ethanolic extract of P. betle exhibited the highest antimicrobial activities, having the inhibition zone of 8.00?0.00 to 24.33?0.58 mm. The MIC and MBC values of the P. betle extract ranged from 0.07 to 1.17 and 0.29 to 9.38 mg/ml, respectively. P. betle extracts also had wide scope of inhibition against all bacterial species tested, and particularly displayed promising inhibitory effects against Staphylococcus aureus, one of the most significant infectious and drug-resistant bacteria in dairy farming. These results will be used for further development of natural therapeutic products for bovine mastitis treatment and control, which is hoped to be alternative products to commercial antibiotics.