The vital role of CovS in the establishment of Streptococcus equi subsp.zooepidemicus virulence

Streptococcus equi subsp.zooepidemicus(SEZ)is an important zoonotic agent.Here,a virulence-attenuated strain M35246 derived from natural variation of wild-type SEZ ATCC35246 was found.M35246 showed a deletion of 25contiguous genes as well as a loss-of-function mutation in covS.Subsequently,a 25-gene-deleted strain(ΔPI),a covS-mutant strain(Mcov S),and relevant complementary strains were constructed and investigated.M35246 and Mcov S were significantly less encapsulated and exhibited poorer anti-phagocytic capacity compared to wild-type SEZ.McovS was significantly more sensitive toβ-lactams,aminoglycosides,macrolides,and lincosamides than wild-type SEZ.M35246,McovS,andΔPI exhibited an increase in median lethal dose(LD_(50))in mice by 10~5,10~5,and 5 times when compared to wild-type SEZ,respectively.Neither M35246 nor McovS were isolated from mice 48 h after being challenged with approximately 2000 times the LD_(50)of wild-type SEZ.Transcriptome analysis showed that 668 significantly differentially expressed genes existed between McovS and wild-type SEZ.Numerous virulence factor-encoding genes and anabolicrelated genes in McovS that were involved in anti-phagocytosis,capsule formation,pathogenicity,and antibiotic resistance were downregulated significantly relative to the wild-type strain.This study revealed that the CovS plays a vital role in the establishment of SEZ virulence.

Identification and Characterization of Putative Virulent Genes in Streptococcus equi ssp. zooepidemicus

Suppression subtractive hybridization （SSH） was performed with virulent strain ATCC35246 and avirulent strain ST171 to identify novel genes associated with virulence in Streptococcus equi ssp. zooepidemicus （SEZ）. There were fourteen genomic regions that only presented in virulent strain ATCC35246. These regions encoded 14 proteins, some of them were homologous to proteins associated with cellular surface structure, molecular synthesis, energy metabolism, regulation, transport systems, and other unknown functions. Primers for 6 particular regions were designed from the already published SEZ sequence. Then, we used PCR to evaluate the distribution and conservation of these 6 DNA fragments in various SEZ strains collected from different sources, regions, groups, and times. The results showed that these 6 DNA fragments were widely distributed in SEZ strains, yet they were not existence in the avirulent strain ST171. Moreover, these fragments could not be detected in other Streptococcus groups.