FDA to Monitor Antimicrobial Use in Livestock—Experts Push for Further Action

May 19, 2016
Amy Karon, DVM, MPH

Companies that sell or distribute antibiotics for use in food animals will soon have to report sales by animal species, according to a revised rule finalized on May 10 by the US Food and Drug Administration (FDA).

Companies that sell or distribute antibiotics for use in food animals will soon have to report sales by animal species, according to a revised rule finalized on May 10 by the US Food and Drug Administration (FDA).

Drug sponsors are already required to report sales of antibiotics used in farming, but the rule revision aims to clarify exactly how these drugs are used and limit the indiscriminate use of medically important antimicrobials, FDA officials said in a press release. The information “will further enhance FDA’s ongoing activities related to slowing the development of antimicrobial resistance,” added William Flynn, DVM, MS, deputy director for science policy in the FDA’s Center for Veterinary Medicine.

The FDA, the US Department of Agriculture, and the US Centers for Disease Control and Prevention (CDC) also plan to look more closely at antibiotic use and resistance on farms in order to paint “a comprehensive and science-based picture of antimicrobial drug use and resistance in animal agriculture,” according to the FDA.

A Global Emergency

The FDA’s announcement comes as scientists worldwide call for major changes in the agricultural use of antibiotics in order to avert the global spread of pan-resistant bacteria.

That scenario is not the stuff of science fiction— in November 2015, researchers in China reported that gram-negative bacteria from farms and patients were resistant to colistin, a polymyxin used as a last resort when all other antibiotics have failed. Even worse, the resistance mutation (known as mcr-1) was located on plasmids, which bacteria readily share with each other through horizontal gene transfer. Colistin is used in animal feed in China, and the prevalence of the resistance mutation correlated with its use in farm animals, the authors wrote in The Lancet.

In the United States, where farming accounts for 80% of antibiotic use, antibiotic-resistant bacteria cause at least 2 million illnesses and 23,000 deaths in humans every year, according to the CDC.

“Despite substantial efforts in antibiotic development, infection control, and human antibiotic stewardship, antibiotic resistance continues to propagate,” warned Michael Nailor, PharmD, of the University of Connecticut, together with his colleagues, in a recent position statement from the Society of Infectious Diseases Pharmacists. Antibiotic stewardship programs that focus exclusively on humans fail to address the bulk of the problem, they wrote in the April 2016 article published in Pharmacotherapy.

Antibiotics have been used as growth promoters since the early 1950s, when scientists learned that adding them to feed hastened growth rates in food animals. Dr. Nailor and his associates noted that the practice persists today, more than four decades after experts first warned about risks to human health.

Several factors facilitate the spread of bacterial resistance from farms to humans, they added. Many antibiotics used in agriculture have similar structures as those used in humans, so a mutation that confers a selective advantage on the farm may also do so in the hospital. Furthermore, resistant bacteria can spread from food animals to humans through a variety of routes, including direct contact, environmental contamination, and contamination of food products. Finally, antibiotics themselves can end up in the commercial food supply. In 2011, the USDA Food Safety and Inspection Service identified antibiotic residues in about 1% of milk, meat, and eggs sampled, and 0.16% of samples exceeded USDA’s maximum limit for antibiotic residue — a small but significant percentage, given the widespread consumption of these foods.

A Call for Action

The Society for Infectious Disease Pharmacists calls for actions well beyond the FDA’s rule revision. First, farms should minimize the use of all antibiotics that the FDA considers harmful to human health, they assert. In addition, farmers should be required to report all antibiotic use, FDA should implement mandatory labeling changes to prevent the use of antibiotics as growth promoters, and funds should be allocated to study how the use of antibiotics in agriculture affects human health and alternative ways to increase food production.

“Given that the vast majority of antibiotics used worldwide are for nontherapeutic agricultural purposes and that the transfer of antibiotic resistance to humans is a well-documented consequence, an increased effort to curb antibiotic use in agriculture is critical to a national and global strategy of combating antibiotic resistance,” the authors conclude.

The researchers who reported colistin resistance in China agree. “In the absence of new agents effective against resistant Gram-negative pathogens, the effect on human health by mobile colistin resistance cannot be underestimated,” they write. “It is imperative that surveillance and molecular epidemiological studies on the distribution and dissemination of mcr-1 among Gram-negative bacteria in both human and veterinary medicine are initiated, along with re-evaluation of the use of polymyxins in animals.”

Dr. Amy Karon earned her doctorate in veterinary medicine and master’s degrees in public health and journalism from the University of Wisconsin-Madison. She was an infectious disease epidemiologist and “disease detective” (EIS officer) with the Centers for Disease Control and Prevention before becoming a full-time medical writer. She lives in the San Francisco Bay area, where she volunteers for the local Humane Society.