In Vitro Antimicrobial Potential of Medicinal Plant Extracts and Their Combinations Against Mastitis-Causing Bacteria in Dairy Cows.

Abstract

Mastitis in dairy cows, caused by pathogens such as <i>Staphylococcus aureus</i>, <i>Escherichia coli</i>, and <i>Candida albicans</i>, leads to substantial economic losses and contributes to antimicrobial resistance, emphasizing the need for natural alternatives. This study assessed the phytochemical composition, antioxidant activity, and in vitro antimicrobial effects of ethanol extracts from ten medicinal plants, including <i>Populus balsamifera</i> buds, <i>Syzygium aromaticum</i>, and <i>Humulus lupulus</i>, as well as two multi-component plant mixtures and commercial products against reference strains and field isolates of mastitis pathogens. Extracts exhibited total phenolic contents ranging from 2.5 to 43.0 mg GE/g, with <i>Populus balsamifera</i> and <i>Syzygium aromaticum</i> demonstrating the strongest DPPH radical scavenging activity (IC₅₀ 1.89-2.9 mg/g extract). Disc diffusion assays demonstrated broad-spectrum inhibition, particularly for <i>Populus balsamifera</i> (15.1-19.1 mm inhibition zones) and <i>Humulus lupulus</i> (9.0-18.4 mm) against key pathogens; phenolic and flavonoid contents positively correlated with antimicrobial activity (r = 0.63-0.99, <i>p</i> < 0.001). Multi-component mixtures provided consistent broad-spectrum effects (12.6-17.2 mm). These phenolic-rich plant extracts represent promising alternatives to reduce antibiotic use in dairy mastitis management.