Characterization of vancomycin-resistant Enterococcus faecium isolated from swine in three Michigan counties

Area of Science:

• Microbiology
• Veterinary Science
• Public Health

Background:

• Vancomycin-resistant enterococci (VRE) are significant causes of hospital-acquired infections.
• VRE are uncommon in community settings and previously unidentified in U.S. food animals.
• Enterococcus faecium is a common pathogen, with vancomycin resistance posing a growing threat.

Purpose of the Study:

• To investigate the presence of VRE in humans and animals at Michigan county fairs.
• To characterize VRE isolates, including their resistance mechanisms and genetic relatedness.

Main Methods:

• Fecal specimens (n=360) from humans and various animals were collected from three Michigan county fairs.
• Samples were cultured on Enterococcosel agar with vancomycin (16 µg/ml).
• VRE isolates were confirmed using vancomycin Minimum Inhibitory Concentration (MIC) testing, vanA gene detection, Pulsed-field gel electrophoresis (PFGE), and Multilocus Sequence Typing (MLST).

Main Results:

• Vancomycin-resistant Enterococcus faecium (VREF) was isolated from six pigs; no VREF was found in humans or other animal species.
• All VREF isolates exhibited high-level vancomycin resistance (MIC ≥256 µg/ml) and carried the vanA gene.
• PFGE indicated high similarity (>80%) among VREF isolates, and MLST identified sequence types (ST5, ST6, ST185) belonging to clonal complex 5 (CC5).

Conclusions:

• This study reports the first identification of VRE in food animals in the United States, specifically among pigs in Michigan.
• The findings demonstrate the dissemination of genetically related VREF strains within pig populations.
• The presence of VREF in pigs raises concerns about potential transmission pathways and the broader One Health implications.