In Vitro Antibacterial Activities of Fosfomycin against <i>Escherichia coli</i> Isolates from Canine Urinary Tract Infection
2024
Nattha Jariyapamornkoon | Suphachai Nuanualsuwan | Nipattra Suanpairintr
Fosfomycin is a bactericidal drug recommended as an alternative treatment for canine bacterial cystitis, particularly in cases involving multidrug-resistant (MDR) infections when no other options are available. In this study, minimum inhibitory concentration (MIC) and mutant prevention concentration (MPC) of fosfomycin were determined against 79 clinical <i>E. coli</i> isolates using the agar dilution method. The susceptibility rate of <i>E. coli</i> to fosfomycin was 86.06%, with MIC<sub>50</sub> and MIC<sub>90</sub> values of 4 mg/L and 96 mg/L, respectively. MPC<sub>50</sub> and MPC<sub>90</sub> values were 64 mg/L and 192 mg/L. Using pharmacokinetic (PK) data from dogs given a single 80 mg/kg oral dose of fosfomycin, the area under the curve per MIC<sub>50</sub> (AUC<sub>0–24</sub>/MIC<sub>50</sub>) was 85.79 with time above MIC<sub>50</sub> (T > MIC<sub>50</sub>) exceeding 50%. In urine, the AUC<sub>0–24</sub>/MIC<sub>50</sub> was 10,694.78, and the AUC<sub>0–24</sub>/MPC<sub>90</sub> was 222.81, with T > MPC<sub>90</sub> extending beyond 24 h. Therefore, fosfomycin exhibited significant antibacterial activity against canine uropathogenic <i>E. coli</i>, including MDR strains, at concentrations below the susceptible MIC breakpoint. However, the high MPC values, especially the MPC<sub>90</sub>, indicate the critical importance of performing susceptibility testing for fosfomycin and maintaining ongoing resistance monitoring.
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