In vivo evaluation of mutant selection window of cefquinome against Escherichia coli in piglet tissue-cage model

BACKGROUND: The resistance of cephalosporins is significantly serious in veterinary clinic. In order to inhibit the bacterial resistance production, the mutant selection window (MSW) hypothesis with Escherichia coli (E. coli) ATCC 25922 exposed to cefquinome in an animal tissue-cage model was investigated. RESULTS: Localized infection with E. coli was established in piglets, and the infected animals were administrated intramuscularly with various doses and intervals of cefquinome to provide antibiotic concentrations below the MIC(99), between the MIC(99) and the mutant prevention concentration (MPC), and above the MPC. E. coli lost susceptibility when drug concentrations fluctuated between the lower and upper boundaries of the window, which defined in vitro as the MIC(99) (0.06 μg/mL) and the MPC (0.16 μg/mL) respectively. For PK/PD parameters, there were no mutant selection enrichment when T>MIC(99) was ≤ 25% or T>MPC was ≥ 50% of administration interval. When T>MIC(99) was > 25% and T>MPC was <50% of administration interval, resistance selection was observed. When AUC(24 h)/MIC(99) and AUC(24 h)/MPC were considered, the mutant selection window extended from 32.84 h to 125.64 h and from 12.83 h to 49.09 h, respectively. CONCLUSIONS: These findings demonstrate that the MSW exists in vivo for time-dependent antimicrobial agents, and its boundaries fit well with those determined in vitro. Maintenance of antimicrobial concentrations above the MPC for > 50% of administration interval is a straightforward way to restrict the acquisition of resistance in this tissue cage model. This situation was achieved with daily intramuscular doses of 1 mg cefquinome/kg body weight.