Antibiotic Resistance from Animal Agriculture: Foodborne Illness and Medical Care

The Physicians Committee
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Antibiotic Resistance from Animal Agriculture: Foodborne Illness and Medical Care

A Report from the Physicians Committee for Responsible Medicine
September 2011

Bacteria Acquire Antimicrobial Resistance

Genetic mutations occur on a continuing basis in all life forms, including bacteria. Some mutations confer new properties to the microorganisms, such as the ability to inactivate an antibiotic drug. Continued administration of antimicrobial agents exerts a selective pressure to the exposed bacteria population, allowing those that have developed resistance to thrive, while reducing or eliminating the remainder. Over time, bacteria may undergo additional mutations, which further enhance their resistance.

Once a resistance gene develops, it can be transmitted to other bacteria through a mechanism called gene transfer. Gaining the antimicrobial resistance trait enables the bacteria to survive and even flourish under farm conditions where antibiotics are routinely administered.

Antibiotic-resistant strains can then spread to humans. In the slaughter process, animal feces and body fluids may contaminate the muscle tissue that is delivered to consumers. Livestock workers also acquire bacterial infections through direct contact of animals, carcasses, and manure. A study showed that poultry workers were 32 times more likely to have gentamicin-resistant E. coli, compared with other people in their community, who in turn, are at high risk of becoming victims of second-hand infections.12 A third route of dissemination of antimicrobial resistant bacteria is through environmental carriers—transfer via waterways, as well as via insects, rodents, and birds.