Susceptibility breakpoint for cefquinome against Escherichia coliand Staphylococcus aureusfrom pigs

Cefquinome is the only fourth-generation cephalosporin used solely for veterinary applications. In this study, we established the wild-type cut-off (COWT) and pharmacokinetic/pharmacodynamic cut-off (COPD) of cefquinome against Escherichia coliand Staphylococcus aureus.A total of 210 E. coliand 160 S. aureusisolates were collected from pigs in Guangdong Province between 2014 and 2018. The minimum inhibitory concentrations (MICs) were determined using a microdilution broth method. MIC50and MIC90were 0.06 and 0.25 μg mL−1for E. coliand 0.5 and 1 μg mL−1for S. aureus,respectively. Statistical analysis and the ECOFFinder Program showed that the COWTfor cefquinome against E. coliand S. aureuswere 0.125 and 2 μg mL−1, respectively. The resistance rates were 11.9% for E. coliand 6.25% for S. aureus.Based on a 5000-subject Monte Carlo simulation, the COPDvalue for cefquinome against E. coiland S. aureuswas 0.25 μg mL−1under the recommended dose (2 mg kg−1, twice a day for 3 days), confirming that infections caused by strains with MIC≤0.25 μg mL−1could be effectively treated. Following adjustment of the dosing regimen to 4.5 mg kg−1, effective treatment (>90) was achieved for S. aureusinfections with MIC901 μg mL−1. This susceptibility breakpoint determination is significant for resistant surveillance and cefquinome dosage guidance against E. coliand S. aureusin pigs.