Bacterial Pathogens of Bovine Mastitis: Prevalence, Antimicrobial Susceptibility, and Sensitivity to Caesalpinia sappan Both In Vitro and In Vivo Studies

Mastitis is a major infectious disease that causes significant economic losses in the dairy industry. Current control programs primarily rely on antimicrobials, contributing to the growing concerns of the resistance situation and drug residues in milk. This study aimed to identify the bacterial pathogens responsible for subclinical/clinical bovine mastitis, assess their antimicrobial resistance profiles, and evaluate the antimicrobial effects of <i>Caesalpinia sappan</i> in treating mastitis through both in vitro and in vivo studies. A total of 138 bacterial isolates, representing 40 species, were identified from 100 milk samples collected from dairy cows under the Maejo Cooperative Group in Chiang Mai, Thailand, between May 2021 and February 2022. The most prevalent species was <i>Escherichia coli</i> (10.87%), followed by <i>Bacillus cereus</i> (9.42%) and <i>Staphylococcus sciuri</i> (7.97%). The highest resistance rates were observed for penicillin (65.21%), followed by streptomycin and lincomycin (61.59%). Nine isolates resisted all 18 antimicrobials tested. The average minimum inhibitory concentration (MIC) of <i>C. sappan</i> against the identified pathogens ranged from 0.63 to 17.68 mg/mL, with the highest MIC observed against <i>Pseudomonas luteola</i>. In the animal experiment, treatment with a prototype of an intramammary infusion compound primarily formulated from <i>C. sappan</i> significantly reduced the total bacterial count and California Mastitis Test (CMT) scores (<i>p</i> < 0.01). These results suggest that <i>C. sappan</i> exhibits antimicrobial efficacy against various mastitis bacteria and could serve as a potential alternative treatment to control bovine mastitis in dairy cattle within the study region.