Levofloxacin efficacy against E. coli isolated from pet rabbits: pilot study

Escherichia coli are commensals, but some strains can be pathogenic. Enteropathogenic E. coli causes diarrhea that could be lethal for companion animals, including pet rabbits. Enrofloxacin is a first-choice antimicrobial agent, although microbial resistance to this drug has been reported. Levofloxacin (LVFX) is a third-generation broad-spectrum fluoroquinolone (FQ) antimicrobial, approved for human medicine and is recommended by the International Society for Companion Animals Infectious Diseases as an off-label drug. LVFX in vitro efficacy against E. coli isolated from companion rabbits was evaluated. Rectal swabs were aseptically collected from 6 (two sampling times) clinically healthy companion rabbits with no history of FQ administration. Swabs were seeded on McConkey agar and E. coli presence was confirmed using the VITEK 2 system. Preliminary susceptibility to LVFX was detected with an E-test®. Minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were confirmed with broth microdilution method according to Clinical and Laboratory Standards Institute M100 guidelines. E. coli strain ATCC 25922 was used as a reference. The reference E. coli strain had the MIC of 0.02 µg/mL (susceptible). In the first sampling, three E. coli isolates were identified, two of which showed the MIC > 8 µg/mL (resistant). One LVFX isolate exhibited MIC value of 0.93 µg/mL (intermediate susceptibility). In the second sampling, 6 rabbit samples revealed two E. coli isolates, one of which had the MIC 0.25 µg/mL and MBC 0.5 µg/mL (susceptible), another MIC 1 µg/mL and MBC 2 µg/mL (intermediate susceptibility). The results found are in line with MIC and MBC values reported in other domestic species. Potentially dangerous E. coli were isolated from companion rabbits. LVFX resistant strains were present, despite no history of FQ treatment. Larger isolate sample size is required to evaluate the incidence of carrying E.coli in pet rabbits and to investigate the susceptibility range for LVFX.