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

According to the 2013 "Antibiotic Resistance Threats Report" from the Centers for Disease Control & Prevention, two of the 18 pathogens that are of concern in the U.S. may have a direct link to agriculture — one of them being salmonella.

For the study, 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. The results were published in Critical Reviews in Food Science & Nutrition (volume 57, issue 3). Animals in the reviewed studies included chickens, turkeys, pigs, beef cattle and dairy cows.

According to an announcement from the Animal Health Institute (AHI), which funded the study, the overall prevalence of salmonella and drug resistance found in the systematic review aligns with recent National Antimicrobial Resistance Monitoring System (NARMS) reports. The 2013 NARMS report showed that 81% 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 versus antibiotic-free operations. None of the reviewed studies followed animal-associated antibiotic-resistant isolates from the farm to retail products.

"While there were some studies worth noting in our 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," lead scientist Dr. Kristi Helke with MUSC said.

"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," Helke added.

Dr. Richard A. Carnevale, AHI vice president for regulatory, scientific and international affairs, noted that as of Jan. 1, the agriculture industry "took an important step in promoting the effectiveness of antibiotics" through its compliance with new Food & Drug Administration mandates Guidance #209 and Guidance #213, "which eliminate the use of medically important antibiotics for growth promotion purposes and 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."

Carnevale added, "We support this research and more research like it to promote a positive impact on public health."

Dr. Bernadette Marriott, principal investigator on the study who also is with MUSC, explained, "Our research results underscore the need for both veterinarians and physicians to work together as we advance toward solutions to concerns about antibiotic resistance."

A similar systematic review of campylobacter was conducted previously, and the findings were published in 2016.