Glycopeptide resistance in Enterococcus faecium strains from animals and humans

The isolation of vancomycin (glycopeptide)-resistant Enterococcus strains (GRE) from animals and from foods has led to the assumption that animals could be a reservoir of GRE, mainly Enterococcus faecium, which cause important problems in hospitals. The use of the glycopeptide antibiotic avoparcin as a growth promoter in farm animals is thought to have been responsible for the occurrence of GRE in humans in Europe. Glycopeptide-resistant E. faecium have been shown to be most prevalent in broiler chickens, the type of animal in which avoparcin has been used most widely. Some differences in prevalence between countries with different antibiotic-feed policies have been documented, but comparisons are hampered by the different detection methods applied. Vancomycin supplementation of selective enrichment media and plates as used most frequently in Europe strongly influences isolation results. In the United States, where glycopeptides have not been incorporated in animal feed, hospital usage is considered to be the sole cause of the relatively high prevalence of nosocomial infections caused by GRE. Investigators have been looking in many countries for evidence of the transfer of GRE or the transfer of the genes encoding vancomycin resistance from animals to humans. Although resistance genes in E. faecium strains from animals and humans are often similar, the bacteria themselves do not appear to spread readily between different animal host species and humans. To date, no final conclusions on the possible spread of GRE or glycopeptide resistance genes from animals to humans can be drawn.