In vitro antibacterial activity of levofloxacin against Gram-negative bacteria isolated from canine urinary tract infections https://doi.org/10.12982/VIS.2026.083
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Abstract
Urinary tract infection (UTI) is a common bacterial disease in dogs, and the increasing prevalence of antimicrobial resistance among uropathogens has complicated therapeutic management. This study aimed to evaluate the in vitro antibacterial activity of levofloxacin against Gram-negative bacteria isolated from dogs with UTIs. A total of 284 Gram-negative bacterial isolates were obtained from urine samples of dogs diagnosed with UTIs. Bacterial identification was performed using Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS). The in vitro antibacterial activity of levofloxacin was evaluated by determining the Minimum inhibitory concentration (MIC) and Mutant prevention concentration (MPC) using the agar dilution method. Low susceptibility rates were observed among Enterobacterales, including Escherichia coli (E. coli) (26.96%), Klebsiella pneumoniae (K. pneumoniae) (31.37%), and Proteus mirabilis (P. mirabilis) (36.84%), whereas Pseudomonas aeruginosa exhibited higher susceptibility (72.13%). MPC values were consistently higher than MICs, particularly for E. coli, K. pneumoniae, and P. aeruginosa, suggesting an increased risk of resistance selection at high bacterial densities. Pharmacokinetic/pharmacodynamic (PK/PD) analysis indicated that the standard oral dose of levofloxacin (25 mg/kg) is likely effective only against susceptible strains, with P. mirabilis being the only species to achieve both MIC- and MPC-based PK/PD targets. Although levofloxacin may be effective against certain canine UTI pathogens, its use should be guided by bacterial identification and susceptibility testing. Therefore, levofloxacin should be considered a second-line therapeutic option rather than an empirical first-line treatment for canine UTIs.
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