Oral Presentation The Prato Conference on the Pathogenesis of Bacterial Infections of Animals 2016

Genome-wide identification of virulence-associated genes in Erysipelothrix rhusiopathiae, the causative agent of swine erysipelas (#14)

Yoshihiro Shimoji 1 , Yohsuke Ogawa 1 , Kazumasa Shiraiwa 1 , Sayaka Nishikawa 1 , Masahiro Eguchi
  1. National Institute of Animal Health, National Agriculture and Food Research Organization (NARO), Tsukuba, IBARAKI, Japan

The gram-positive pathogen Erysipelothrix rhusiopathiae can infect a wide variety of animals, including humans and birds. Intracellular survival and replication are key virulence features of E. rhusiopathiae because mutants defective in these attributes are totally avirulent (Microbes infect, 2000). The organism shows reductive genome evolution but possesses an extremely high number of antioxidant factors and phospholipolytic enzymes, many of which may facilitate intracellular survival in phagocytic cells. Thus, it appears that during the evolutionary process, E. rhusiopathiae specifically adapted to intracellular environments of phagocytic cells (J Bacteriol, 2011), yet the underlying mechanisms remain poorly understood.

To identify the genes that may play key roles in intracellular survival, we constructed more than 700, non-redundant transposon mutants from a highly virulent Fujisawa strain. This strain contains a total of 1,704 CDSs. We screened the mutants for virulence attenuation in mice. For each mutant, two mice were subcutaneously inoculated with 108 CFU of bacteria and observed for clinical symptoms and death.

We obtained 21 mutants that were attenuated for virulence. Among them, 17 mutants did not cause any clinical symptoms. However, 4 mutants caused clinical symptoms and death in one mouse. The defined virulence genes included lic genes, which are responsible for decoration of capsule with phosphorylcholine, and the genes encoding transporters/symporters, transcription regulators, and enzymes involved in an amino acid biosynthesis among others. The mutants that had a transposon insertion in a gene encoding for an antioxidant factor or five phospholipolytic enzymes did not affect the virulence, probably due to functional redundancy of these proteins.

It has been demonstrated that the surface molecules, namely capsule and phosphorylcholine, play a critical role in virulence (Infect Immun, 2012). This is probably through receptor interactions between the organism and macrophages. The data in this study may further provide new insights into intracellular survival mechanisms of E. rhusiopathiae.