Spread without known selective pressure of a vancomycin-resistant clone of Enterococcus faecium among broilers

Area of Science:

• Veterinary Microbiology
• Antimicrobial Resistance
• Food Safety

Background:

• Vancomycin-resistant enterococci (VRE) pose a significant threat to public health.
• Increased occurrence of VRE in food-producing animals warrants investigation into transmission dynamics.

Purpose of the Study:

• To document the rise of VRE in Swedish broiler chickens from 2000 onwards.
• To analyze the genetic relatedness of VRE isolates to understand clonal spread.

Main Methods:

• Culturing of broiler caecal content for VRE using vancomycin-supplemented media.
• Species identification, antibiotic susceptibility testing, vancomycin resistance genotyping, MLST, and Tn1546 characterization.

Main Results:

• VRE prevalence in broilers rose from <1% in 2000 to over 40% in 2005, then stabilized below 30% by 2007.
• All isolates were Enterococcus faecium carrying the vanA gene.
• A predominant clone with similar antibiograms, MLST type, and Tn1546 was identified.

Conclusions:

• A single major clone of VRE has spread extensively in Swedish broilers since 2000.
• This clonal expansion occurred despite a lack of obvious environmental selective pressure.
• Findings indicate a need for enhanced surveillance and control measures for VRE in poultry.