Persistence of vancomycin resistance in multiple clones of Enterococcus faecium isolated from Danish broilers 15 years after the ban of avoparcin

Occurrence and diversity of vancomycin-resistant Enterococcus faecium (VREF) were investigated in 100 Danish broiler flocks 15 years after the avoparcin ban. VREF occurred in 47 flocks at low fecal concentrations detectable only by selective enrichment. Vancomycin resistance was prevalently associated to a transferable, non-typeable plasmid lineage occurring in multiple E. faecium clones. Co-selection of sequence type 842 by tetracycline use only partly explained persistence of vancomycin resistance in the absence of detectable plasmid co-resistance and toxin-antitoxin systems.