In recent years, scientists have worried that food animals given antibiotics to promote their growth may be a reservoir of drug-resistant bacteria and resistance genes that could spread to human populations. Now, researchers report in the July issue of Antimicrobial Agents and Chemotherapy that banning antibiotics for this purpose can cause a dramatic reduction in bacterial resistance rates in food animals.
Researchers at the Danish Veterinary Laboratory in Copenhagen tested more than 2500 isolates of enterococcal bacteria from pigs and broiler chickens for antibiotic resistance patterns from 1995 to 2000. They found that during this period, resistance rates to avoparcin (which was banned in Denmark in 1995) plummeted from nearly 73% to just over 5%. Resistance to virginiamycin, which was banned in 1998, dropped from more than 66% in 1998 to less than 40% in 2000.
Stephenson J. Antibiotics and Agriculture. JAMA. 2001;286(6):663. doi:10.1001/jama.286.6.663-JWM10007-2-1