Abstract
To evaluate the effect of antimicrobial susceptibility on outcomes, we compared the minimum inhibitory concentrations (MICs) for Staphylococcus, Streptococcus, and the family Enterobacteriaceae from cured and uncured mastitis cases; milk shipment for uncured cases could not be resumed within 3 weeks after initial clinical examination. A higher MIC(50) of ampicillin and a higher MIC(90) of cefazolin for Enterobacteriaceae isolates were observed for cured rather than uncured cases with differences in ≥2 tubes. Endotoxins are generally released from Enterobacteriaceae upon antimicrobial treatment; their amounts are presumed to be greater in mastitis cases resulting from β-lactam antibiotic-susceptible rather than -resistant microbes. For staphylococcal and streptococcal isolates, the MIC(50) and MIC(90) of β-lactam antibiotics were similar for cured and uncured cases.