The Two-Component Signaling System VraSR _ss Is Critical for Multidrug Resistance and Full Virulence in Streptococcus suis Serotype 2

Abstract

has received increasing attention for its involvement in severe human infections worldwide as well as in multidrug resistance. Two-component signaling systems (TCSSs) play important roles in bacterial adaptation to various environmental stimuli. In this study, we identified a novel TCSS located in serotype 2 (SS2), designated VraSR, which is involved in bacterial pathogenicity and susceptibility to antimicrobials. Our data demonstrated that the gene, located upstream of , shared the same promoter with the TCSS genes, which was directly regulated by VraSR, as shown in electrophoretic mobility shift assays. Notably, YvqF and VraSR constitute a novel multidrug resistance module of SS2 that participates in resistance to certain groups of antimicrobials. Further analyses showed that VraSR inactivation significantly attenuated bacterial virulence in animal models, which, coupled with the significant activation of VraSR expression observed in host blood, strongly suggested that VraSR is an important regulator of SS2 pathogenicity. Indeed, RNA-sequencing analyses identified 106 genes that were differentially expressed between the wild-type and Δ strains, including genes involved in capsular polysaccharide (CPS) biosynthesis. Subsequent studies confirmed that VraSR indirectly regulated the transcription of CPS gene clusters and, thus, controlled the CPS thickness shown by transmission electron microscopy. Decreased CPS biosynthesis caused by deletion subsequently increased bacterial adhesion to epithelial cells and attenuated antiphagocytosis against macrophages, which partially clarified the pathogenic mechanism mediated by VraSR Taken together, our data suggest that the novel TCSS, VraSR, plays critical roles for multidrug resistance and full virulence in SS2.

Identification of an Autorepressing Two-Component Signaling System That Modulates Virulence in Streptococcus suis Serotype 2

“…Macrophage phagocytosis activates TCS genes. The genome of the ZY05719 strain encodes 15 putative TCSs, among which RevS, Salk/SalR, CovR, CiaRH, Ihk/Irr, VirR/VirS, NisK/NisR, 1910HK/RR, and VraSR SS have already been identified to contribute to SS2 virulence (11)(12)(13)(14)(15)(16)(17)(18)(19)(20). To explore the potential roles of the remaining six uncharacterized TCSs in bacterial pathogenicity, murine macrophage-like RAW264.7 cells were applied to coincubate with the SS2 strain ZY05719.…”

“…In addition, the S. suis transcriptional landscape has revealed that genes involved in CPS biosynthesis were upregulated in blood (45). Nevertheless, S. suis CPS-deficient mutants have been reported to adhere to epithelial cells better than the encapsulated parental strain (20,46,47), as CPS might cover adhesins on the bacterial surface (48). Therefore, it has been proposed that S. suis downregulates expression of the capsule for increased adhesion to epithelial cells during the early steps of infection, whereas it upregulates capsule production after entering the bloodstream to counter phagocytosis (49).…”

“…In addition to TCS09HKRR, three other TCSs have already been identified to regulate CPS biosynthesis in the SS2 strains (13,16,20). The orphan response regulator CovR is a global virulence regulator that represses the expression of 193 genes, including that of cps2C and neuA (13), whereas proteomic analysis showed that VirR/VirS contribute to the expression of cps2B, cps2C, and neuC (16).…”

“…TCSs are usually employed to sense and respond to extracellular signals during the infection process (2,9). Bioinformatics analysis of the genome of SS2 strains identified 15 TCSs (10), among which RevS, Salk/SalR, CovR, CiaRH, Ihk/Irr, VirR/VirS, NisK/NisR, 1910HK/RR, and VraSR SS have been reported to regulate the expression of putative virulence factors, mediate multidrug resistance, or alter bacterial metabolism (11)(12)(13)(14)(15)(16)(17)(18)(19)(20), thereby contributing to the adaption of SS2 strains to environmental stimuli. In bacteria, RRs often regulate the transcription of their own operons, which contain cognate sensor HK genes.…”

“…Such autoregulation can be useful if the pathogen needs to respond to environmental changes rapidly (21,22). VraSR SS exhibits positive autoregulation ability, as its own transcription is activated by the regulator protein VraR SS (20). Autorepression is less common than autoactivation among TCSs and appears to be inherent in areas of metabolism for maintaining metabolic homeostasis (22).…”