Establishing the Epidemiological Cut‐Off Value (ECOFF) for Cefquinome Against Staphylococcus aureus Using Standardised MIC Data

Staphylococcus aureus is a major pathogen responsible for a wide range of infections in both animals and humans, and the increasing emergence of antimicrobial resistance highlights the need for effective surveillance tools. Cefquinome, a fourth-generation cephalosporin, is widely used in veterinary medicine for the treatment of infections caused by Gram-positive and Gram-negative bacteria, including S. aureus. In this study, 110 S. aureus strains were isolated from cattle and subjected to minimum inhibitory concentration (MIC) determination using standardised agar dilution and microdilution methods. MIC values were obtained following 24 h incubation in 96-well plates. The MIC distribution was analysed using goodness-of-fit testing and non-linear least squares regression to establish the wild-type cut-off value (COWT). The MIC range for cefquinome against S. aureus was 0.03-2 µg/mL, and the epidemiological cut-off value (ECV) was determined to be 2 µg/mL, encompassing 99.1% of the wild-type population. An MIC value of 0.5 µg/mL covered 95% of the distribution, indicating its potential relevance for resistance monitoring. These findings provide a scientific basis for cefquinome susceptibility interpretation in cattle and support antimicrobial resistance surveillance. Further studies are warranted to develop population pharmacokinetic models for cefquinome in calves to optimise its therapeutic application.