Repeated therapeutic dosing selects macrolide-resistant Campylobacter spp. in a turkey facility

Area of Science:

• Veterinary Microbiology
• Antimicrobial Resistance
• Food Safety

Background:

• Campylobacter is a common poultry pathogen.
• Antimicrobial use in livestock can drive resistance.
• Macrolide resistance in Campylobacter is a growing concern.

Purpose of the Study:

• To assess the impact of therapeutic macrolide (Tylan®) use on macrolide-resistant Campylobacter selection in a large-scale turkey production facility.
• To investigate the persistence and transfer of resistant strains.
• To identify molecular mechanisms of resistance.

Main Methods:

• A large flock (approx. 30,000 turkeys) was monitored from brooding to slaughter.
• One half of the flock received macrolide treatment during the finishing stage, while the other half served as a control.
• Campylobacter prevalence and macrolide resistance levels were assessed.
• Molecular techniques including PCR, RFLP, and 23S rRNA sequencing were used.

Main Results:

• Campylobacter prevalence reached nearly 100% by 4 weeks of age.
• Macrolide treatment led to high levels of macrolide resistance, with Campylobacter coli becoming dominant.
• Resistant strains decreased over time in the absence of the selection agent, suggesting a fitness cost.
• Low-level resistance was found in the control group, indicating treatment correlation.
• A2075G mutation in 23S rRNA and the CmeABC efflux pump were associated with high-level resistance.

Conclusions:

• Macrolide treatment during the grow-out phase promotes antimicrobial resistance in Campylobacter.
• Established resistance can persist and be transferred to final poultry products.
• Prudent antimicrobial use in poultry is crucial to mitigate resistance development and spread.