Impact of antibiotic use in animal feeding on resistance of bacterial pathogens in humans

With the exception of flavomycin and olaquindox, the antibiotics currently used in European countries as feed additives exert a Gram-positive spectrum of activity. Of these, tylosin and virginiamycin are known for cross-resistance to macrolides, lincosamidines and streptogramines, and avoparcin is known for cross-resistance to vancomycin and teicoplanin. The use of avoparcin in animal husbandry creates a potential reservoir of transferable, vanA-mediated glycopeptide resistance in enterococci. A study in a rural area in Germany where vancomycin-resistant enterococci (VRE) were not isolated from infected humans but found in animal husbandry has shown that VRE are disseminated via meat products and are also found in faecal samples of non-hospitalized humans. VRE of different ecological origin from Germany (hospitals, sewage, food, animal husbandry) are polyclonal as evidenced by macrorestriction patterns and multilocus enzyme electrophoresis, suggesting a wide dissemination of the vanA gene cluster. These results confirm earlier observations on the spread of the sat genes, which confer resistance to a streptothricin antibiotic which has only been used in animal feeding. The resistance determinants were later also found in Escherichia coli from human infections and had spread in the absence of selective pressure.