Study on antibiotic use, salmonella shows need for more farm-to-fork research

What are the chances you’d be well on your way to becoming a vet and then realize you were allergic to all animals except for two?

As it turns out, that was the case for researcher Kristi Helke, D.V.M., Ph.D., in the Department of Comparative Medicine at the Medical University of South Carolina. Allergies caused her to switch from her veterinary practice to become a researcher.  

She is part of a team of interdisciplinary scientists at the Medical University of South Carolina and the Charleston VA Medical Center Research Service that recently reviewed published literature for evidence of a relationship between antibiotic use in agricultural animals and drug-resistant foodborne salmonella infections in humans, commonly known as salmonellosis. 

According to the 2013 Antibiotic Resistance Threats Report from the Centers for Disease Control and Prevention, two of the 18 pathogens of concern in the United States may have a direct link to agriculture — one of them being salmonella. Foodborne illness from both drug-sensitive and drug-resistant non-typhoidal salmonella is estimated to sicken 1.2 million Americans annually. The new study — conducted by veterinary and nutrition scientists and an infectious disease physician — reviewed 104 articles in the U.S., Canada, Denmark, Scotland and Ireland over the past five years and has been published in Critical Reviews in Food Science and Nutrition. Animals included in the reviewed studies were chicken, turkeys, pigs, beef cattle and dairy cows.

Helke, who was lead scientist, said having such a wide range of experts on the team was helpful. “It was great. We all learned so much. We were interacting with FDA and CDC as well. It was definitely an interdisciplinary effort.” FDA stands for Food and Drug Administration.

The overall prevalence of salmonella and drug-resistance found in the systematic review aligns with recent National Antimicrobial Resistance Monitoring System, or NARMS, reports. The 2013 NARMS report showed that 81 percent of the salmonella from human infections carried no resistance to any antibiotic, while salmonella resistance rates in animals vary by the antibiotic tested. The findings of this systematic review did lead the team to important concerns about salmonella and demonstrated that more research in this area is needed. For example, six articles showed increased antibiotic resistance in organisms derived from animals, not retail meats, used in conventional farming, versus those from antibiotic-free operations. 

More continuum studies are needed that follow animal-associated antibiotic resistant isolates from farm to retail products, she said.

Helke said while there were some studies worth noting in the review, it is most apparent that there is a greater need for a more robust data collection system and heightened publication expectations in the U.S. for transparency in antibiotic usage in both animals and humans. 

“There is still much more research to be done. The agriculture and health care industries must work hand-in-hand with the scientific community, government regulatory agencies and human health community in order to ensure safe, humane and affordable food sources to the public."

Richard A. Carnevale, V.M.D., is vice president for Regulatory, Scientific and International Affairs at the Animal Health Institute, which funded the study. He said the agriculture community January 1 took an important step in promoting the effectiveness of antibiotics by being in full compliance with new FDA mandates, guidance 209 and 213, that eliminate the use of medically important antibiotics for growth promotion purposes. The mandates also require approval by a licensed veterinarian for all remaining uses in feed through the veterinary feed directive. 

“The proper public health focus — in both humans and animals — should be on using antibiotics only when necessary to fight disease,” he said. “We support this research and more research like it to promote a positive impact on public health."

Principal investigator on the study, Bernadette Marriott, Ph.D., of MUSC, agreed. "Our research results underscore the need for both veterinarians and physicians to work together as we advance toward solutions to concerns about antibiotic resistance."

Helke said more study also is needed about the impact on antibiotic use may be having on plants. “I learned salmonella can actually grow within plant cells. The outbreaks you hear coming from onions and green peppers and such can actually be within the cells of the plant – washing may or may not help that. If you have antibiotic resistant organisms on the farm that are being sprayed onto a field, and it’s being taken up into these plants, that can be causing problems.”

She hopes studies like these will lead to more funding and public awareness about the need to lower antibiotic use on farms and improve crowding conditions of animals that can lead to more sicknesses requiring antibiotic use. In the meantime: “Buy organic when possible, cook your food well and wash your hands.”

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ABOUT THE STUDY AUTHORS

MUSC authors of this study are: Kristi L. Helke, M.A. McCrackin, D.V.M., Ph.D., Ashley Galloway, M.S., R.D., Ann Z. Poole, M.Ed., Cassandra Salgado, M.D., M.S., and Bernadette P. Marriott, Ph.D.. A similar systematic review of campylobacter was also conducted and the findings were published in 2016.

News provided by Animal Health Institute and Medical University of South Carolina.