Lateral exchange of genes for antibiotic production and resistance mediated by global transmission of bacterial pathogen between humans and livestock

Yirui Chen, Clemson University


It is estimated that 60% of human infectious disease is due to zoonotic pathogens. The exchange of bacterial virulence factors driven by lateral gene transfer (LGT) can help indicate possible bacterial transmission among different hosts. Specifically, overlaying the phylogenetic signal of lateral gene transfer among bacteria onto the distribution of respective isolation sources (hosts) can indicate patterns of transmission among these hosts. Here, we apply this approach towards a better understanding of patterns of bacterial transmission between humans and livestock. We utilize comparative genomics to trace patterns LGT for an 11-gene operon for the production of the antibiotic nisin and infer transmission of bacteria among respective host species. A total of 148 bacterial genomes obtained from NCBI were determined to contain the complete operon. Isolated from human, porcine and bovine hosts, these genomes represented six Streptococcus species (Streptococcus suis, Streptococcus agalactiae, Streptococcus pneumoniae, Streptococcus pasteurianus, Streptococcus hyovaginalis, Streptococcus uberis, and Staphylococcus aureus). Phylogenetic analyses of the operon sequences revealed a signature of frequent and recent lateral gene transfer that indicated extensive bacterial transmission between humans and livestock. For 11 isolates, we detected a Tn916-like transposon inserted into the operon. The transposon contained the tetM>/em> gene (tetracycline resistance) and additional phylogenetic analyses again indicated transmission among human and animal hosts. The bacteria possessing the nisin operon were isolated from hosts distributed globally (Netherlands, UK, Belgium, France, Germany, Denmark, USA, Canada, Vietnam, China, Thailand, and Australia), and transmission was unrestricted by geographic distance. These findings possibly reflect both the globalization of the food industry and an increasingly mobile and expanding human population. In addition to concerns regarding zoonosis, these findings also highlight the potential threat to livestock worldwide as a result of reverse zoonosis.