Farm animals from conventional farms and antibiotic free farms both have strains of antibiotic resistant bacteria. In a recent study conducted at North Carolina State University, researchers found identical sequence types of the resistant bacteria Campylobacter coli (C. coli) isolates in pigs raised on conventional farms as well as antibiotic free (ABF) farms.(1) For those that think banning antibiotic use for food production will solve our resistance problems, this study is troubling.
Dr. Siddhartha Thakur collected thousands of samples from pigs and their surrounding environments over several years and performed tests on 200 strains of C. coli to see if those from ABF farms had similar resistance patterns as those using antibiotics.(3) They did.
This study could be interpreted in many ways: 1) antibiotic use does not make a difference in resistance populations, 2) the evil practice of antibiotic use on-farm is impacting ABF farms, 3) some of the ABF farms may have previously used antibiotics and more time is needed for this resistance to disappear, and/or 4) there is another source of resistance other than antibiotic use.
Dr. Thakur proposes 4) another source of resistance. Dr. Thakur’s two studies over several years indicated that the same antibiotic resistant C. coli bacteria were found on conventional and ABF farms. Because the pig populations had never come into contact with each other, Dr. Thakur concluded that the environment must be contributing to the antibiotic resistant bacteria. (2)
It should be noted that C. coli is unique relative to other types of Campylobacter because it is seen primarily in pigs and it has shown higher levels of resistance. Campylobacter is a leading cause of food borne illness in the United States and has been found in populations of swine, cattle, and poultry. However, cattle and poultry usually shed Campylobacter jejuni (C. jejuni), whereas swine are the main source of Campylobacter coli (C. coli).(1) The scientists at NC State attributed the higher resistance to higher frequencies of recombination in C. coli. Recombination in bacteria is a process in which genetic material is transferred between cells, which allows for fast movement of newly evolved genes.
"In the case of ABF pigs, the environment plays an important role in their exposure to these resistant strains," Thakur says. "If the environment itself, and not the pig, is serving as a reservoir for C. coli, then we will most probably continue to find resistant bacteria populations, regardless of a producer's antimicrobial use." (2)
If Dr. Thakur’s analysis and conclusion are correct, then on farm antibiotic use is unlikely to be increasing any human health risk to C. coli. However, the question of antibiotic resistance must be constantly evaluated on a case-by-case (bug-drug) basis.
1. Quintana-Hayashi MP, Thakur S (2012) Phylogenetic Analysis Reveals Common Antimicrobial Resistant Campylobacter coli Population in Antimicrobial-Free (ABF) and Commercial Swine Systems. PLoS ONE 7(9): e44662. doi:10.1371/journal.pone.0044662
2. PhysOrg.com. 2012. Antibiotic-resistant pathogens persist in antibiotic-free pigs. http://phys.org/news/2012-09-antibiotic-resistant-pathogens-persist-antibiotic-free-pigs.html
3. Gabbett, R. J. 2012. Research finds antibiotic-resistance in antibiotic-free pigs. https://www.meatingplace.com/Industry/News/Details/36128