Comparative genome analysis of Erysipelothrix rhusiopathiae isolated from domestic pigs and wild boars suggests host adaptation and selective pressure from the use of antibiotics

The disease erysipelas caused by Erysipelothrix rhusiopathiae (ER) is a major concern in pig production. In the present study the genomes of ER from pigs (n=87), wild boars (n=71) and other sources (n=85) were compared in terms of whole-genome SNP variation, accessory genome content and the presence of genetic antibiotic resistance determinants. The aim was to investigate if genetic features among ER were associated with isolate origin in order to better estimate the risk of transmission of porcine-adapted strains from wild boars to free-range pigs and to increase our understanding of the evolution of ER. Pigs and wild boars carried isolates representing all ER clades, but clade one only occurred in healthy wild boars and healthy pigs. Several accessory genes or gene variants were found to be significantly associated with the pig and wild boar hosts, with genes predicted to encode cell wall-associated or extracellular proteins overrepresented. Gene variants associated with serovar determination and capsule production in serovars known to be pathogenic for pigs were found to be significantly associated with pigs as hosts. In total, 30 % of investigated pig isolates but only 6 % of wild boar isolates carried resistance genes, most commonly tetM (tetracycline) and lsa(E) together with lnu(B) (lincosamides, pleuromutilin and streptogramin A). The incidence of variably present genes including resistance determinants was weakly linked to phylogeny, indicating that host adaptation in ER has evolved multiple times in diverse lineages mediated by recombination and the acquisition of mobile genetic elements. The presented results support the occurrence of host-adapted ER strains, but they do not indicate frequent transmission between wild boars and domestic pigs. This article contains data hosted by Microreact.