Characterization of florfenicol resistance among calf pathogenic Escherichia coli

Area of Science:

• Veterinary Microbiology
• Molecular Biology
• Antimicrobial Resistance

Background:

• Florfenicol is a crucial antibiotic used in veterinary medicine.
• Antimicrobial resistance in pathogenic bacteria like Escherichia coli poses a significant threat to animal health.
• The floR gene has been implicated in florfenicol resistance, but its precise mechanism requires further elucidation.

Purpose of the Study:

• To clone and characterize the floR gene from calf pathogenic Escherichia coli.
• To investigate the role of the floR gene in florfenicol accumulation and efflux in E. coli.
• To determine if florfenicol resistance mediated by floR involves an active efflux mechanism.

Main Methods:

• Cloning of three floR genes from calf pathogenic E. coli strains.
• Construction of a floR gene-JM109 E. coli expression system.
• Quantification of florfenicol accumulation using high-performance liquid chromatography (HPLC).
• Assessment of florfenicol accumulation in the presence and absence of a proton motive force blocker.

Main Results:

• The floR gene yielded a 1356-bp fragment encoding 404 amino acids, with conserved motifs of 12-transmembrane efflux pumps.
• HPLC analysis revealed significantly lower florfenicol accumulation in floR-expressing resistant strains compared to susceptible strains.
• Inhibition of proton motive force with a blocker nearly reversed the observed difference in florfenicol accumulation.

Conclusions:

• The floR gene confers florfenicol resistance in calf pathogenic E. coli.
• Florfenicol resistance mediated by the floR gene is primarily due to active efflux of the antibiotic.
• Understanding this efflux mechanism is critical for managing florfenicol resistance in veterinary settings.