Plant-derived antimicrobials as sustainable alternatives to antibiotics: Evaluation of Piper betle L. and Bauhinia scandens L. against multidrug-resistant zoonotic mastitis pathogens from dairy cattle

Antimicrobial resistance (AMR) among bovine mastitis pathogens poses a growing challenge to dairy production and public health, particularly in smallholder systems with extensive antibiotic use. This study investigated antimicrobial resistance profiles and evaluated the in vitro antibacterial activity of extracts from Piper betle L. and Bauhinia scandens L. against 11 field isolates of Staphylococcus and Streptococcus species among 30 mastitis milk samples collected from dairy cows in Ratchaburi Province, Thailand. Bacterial identification and susceptibility testing were performed using the VITEK® 2 Compact system. Multidrug resistance was defined according to standard criteria. Antibacterial activity of ethanolic extracts was assessed using minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assays following CLSI guidelines. Multidrug resistance was observed in the limited number of isolates examined, particularly in Streptococcus uberis , while Staphylococcus spp. showed limited resistance, and no methicillin-resistant Staphylococcus aureus was detected. Both extracts inhibited all Gram-positive isolates, with MIC values ranging from 0.26 to 6.3 mg/mL among the tested isolates. Bauhinia scandens L. tended to exhibit lower MIC values (as low as <260 μg/mL), whereas Piper betle L. demonstrated comparatively stronger bactericidal activity, with MBC values ranging from 4800 to 12,656 μg/mL. Higher concentrations were required to inhibit multidrug-resistant S. uberis . Compared with conventional antibiotics, the extracts showed relatively lower antibacterial potency under the tested conditions. These findings suggested that the studied plant extracts possess moderate antibacterial activity and may serve as potential plant-based complementary alternatives to antibiotics in mastitis management. However, given the limited number of isolates analyzed, these results should be interpreted as preliminary. Their application could contribute to reducing antibiotic use and mitigating AMR in dairy systems pending further validation. Further in vivo validation and phytochemical characterization are warranted.