Abstract
Bovine mastitis has a high morbidity rate and causes significant economic losses due to milk wastage and antimicrobial use. Mastitis is treated with antimicrobial agents, but criteria for disk diffusion tests for pathogens that cause bovine mastitis in Japan are lacking. In this study, we used a simplified agar disk diffusion (ADD) method that is easy to implement in clinical practice to develop breakpoints for bovine mastitis–associated organisms and generate a corresponding antibiogram. We established new breakpoints for a simplified ADD method for Staphylococcus aureus, coagulase-negative Staphylococcus (CNS), Streptococcus uberis, Streptococcus spp. (except for S. uberis), and Klebsiella spp. We also revalidated previously reported breakpoints against Streptococcus spp. and E. coli. The antibiogram showed that the susceptibility rates of Streptococcus spp. (excluding S. uberis) to marbofloxacin in eastern Japan were significantly lower than those in Hokkaido and western Japan (P < 0.01). The susceptibility rate of E. coli to oxytetracycline (OTC) in eastern Japan was significantly lower than that in Hokkaido (P < 0.01). Low susceptibility rates were observed for ampicillin (ABPC) and erythromycin among CNS strains, OTC among S. uberis strains, and cefazolin, cefuroxime, and ABPC among Klebsiella spp. strains. The use of breakpoints in the simplified ADD method in clinical practice should promote the prudent use of antimicrobial agents. In cases of acute mastitis with systemic symptoms in which antimicrobial agents must be administered prior to susceptibility testing, the antibiogram can be used as a criterion for determining the drug of choice.
© 2025 Japanese Journal of Veterinary Research Editorial Committee, Faculty of Veterinary Medicine, Hokkaido University
