Natural horizontal gene transfer of antimicrobial resistance genes in Campylobacter spp. from turkeys and swine

Authors: GUERNIER-CAMBERT, VANINA - Oak Ridge Institute For Science And Education (ORISE); Trachsel, Julian; MAKI, JOEL - Oak Ridge Institute For Science And Education (ORISE); QI, JING - Shandong Academy Of Agricultural Sciences; SYLTE, MATTHEW - Animal And Plant Health Inspection Service (APHIS); HANAFY, ZAHRA - North Carolina State University; KATHARIOU, SOPHIA - North Carolina State University; Looft, Torey

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2021
Publication Date: 9/27/2021
Citation: Guernier-Cambert, V., Trachsel, J.M., Maki, J.J., Qi, J., Sylte, M.J., Hanafy, Z., Kathariou, S., Looft, T.P. 2021. Natural horizontal gene transfer of antimicrobial resistance genes in Campylobacter spp. from turkeys and swine. Frontiers in Microbiology. 12(1). Article e732969. https://doi.org/10.3389/fmicb.2021.732969.
DOI: https://doi.org/10.3389/fmicb.2021.732969

Interpretive Summary: Campylobacter bacteria are commonly found in the intestinal tract of poultry and waterfowl, but rarely causes clinical disease in birds. However, in humans, undercooked contaminated poultry is a major source of intestinal infections. When infected, most patients experience mild enteritis with diarrhea, and the disease is usually self-limiting without the need for intervention. However, some patients experiencing severe disease will require antibiotic treatment. In recent years, there has been a rise in antibiotic-resistant Campylobacter, which can severely limit treatment options. The identification of factors contributing to antibiotic resistance spread in Campylobacter, especially in the natural gut environment, will inform the development of control strategies along the food supply chain. Thus, we investigated the natural transmission of resistance genes from one Campylobacter bacteria to another. When culturing various pairs of Campylobacter together in a flask, we detected four individual events of antibiotic resistance gene transfer from one strain to another. When the same pairs of Campylobacter were administered to turkeys orally, only one resistance transfer was detected. Overall, we found that resistance genes can be transferred from one Campylobacter to another, including within Campylobacter’s natural environment, i.e. the gut of turkeys. This study provides evidence that antibiotic resistance can naturally spread between Campylobacter, and control strategies need to consider minimizing transfer events to limit the spread of antimicrobial resistance.

Technical Abstract: Antibiotic-resistant Campylobacter constitutes a serious threat to public health. The clonal expansion of resistant strains and/or the horizontal spread of resistance genes to other strains and species can hinder the clinical effectiveness of antibiotics to treat severe campylobacteriosis. Still, gaps exist in our understanding of the risks of acquisition and spread of antibiotic resistance in Campylobacter. While the in vitro transfer of antimicrobial resistance genes between Campylobacter species via natural transformation has been extensively demonstrated, experimental studies have favored the use of naked DNA to obtain transformants. In this study, we used experimental designs closer to real-world conditions to evaluate the possible transfer of antimicrobial resistance genes between Campylobacter strains of the same or different species (C. coli or C. jejuni) and originating from different animal hosts (swine or turkeys). This was evaluated in vitro through co-culture experiments and in vivo with dual-strain inoculation of turkeys, followed by whole genome sequencing of parental and newly emerged strains. In vitro, we observed four independent horizontal gene transfer events leading to the acquisition of resistance to beta-lactams (blaOXA), aminoglycosides (aph(2”)-If and rpsL) and tetracycline (tet(O)). Observed events involved the displacement of resistance-associated genes by a mutated version, or the acquisition of genomic islands harboring a resistance determinant by homologous recombination; we did not detect the transfer of resistance-carrying plasmids even though they were present in some strains. In vivo, we recovered a newly emerged strain with dual resistance pattern and identified the replacement of an existing non-functional tet(O) by a functional tet(O) in the recipient strain. Whole genome comparisons allowed characterization of the events involved in the horizontal spread of resistance genes between Campylobacter following in vitro co-culture and in vivo dual inoculation. Our study also highlights the potential for antimicrobial resistance transfer across Campylobacter species originating from turkeys and swine, which may have implications for farms hosting both species in close proximity.