Roles of SPI-2 T3SS effectors in virulence ofCholeraesuis and Construction of a triple-gene mutant vaccine strain.

Abstract

Effector protein functions of Type III secretion system (T3SS) encoded bypathogenicity islands 2 (SPI-2) have not been fully characterized inserovar Choleraesuis. This study characterized 21 effectors of SPI-2 T3SS ofin terms of macrophage survival and virulence in mice via construction of various gene mutant strains. Eight effector genes including,, andcontributed to bacterial survival in macrophage cell line RAW264.7; whereas onlyalso promoted bacterial virulence in mice like other three effector genes, and. The mutant strain, Δ, Δ, Δ, or Δ, led to higher mouse survival compared to the wild-type strain post-oral infection, while their bacterial loads in spleen and liver were not reduced except the Δthat was undetectable in mouse tissues. Then, the triple-gene mutant strain ΔΔΔwas constructed and found to be virulence attenuated with a compromised colonization ability. Finally, immunization of this mutant orally induced robust serum IgG responses and provided 40% protection against lethalchallenge. Our study highlights the critical role of four SPI-2 T3SS effectors inpathogenesis.