VraR Binding to the Promoter Region of agr Inhibits Its Function in Vancomycin-Intermediate Staphylococcus aureus (VISA) and Heterogeneous VISA

Abstract

Acquisition of vancomycin resistance in Staphylococcus aureus is often accompanied by a reduction in virulence, but the mechanisms underlying this change remain unclear. The present study was undertaken to investigate this process in a clinical heterogeneous vancomycin-intermediate S. aureus (hVISA) strain, 10827; an hVISA reference strain, Mu3; and a VISA reference strain, Mu50, along with their respective series of vancomycin-induced resistant strains. In these strains, increasing MICs of vancomycin were associated with increased expression of the vancomycin resistance-associated regulator gene (vraR) and decreased expression of virulence genes (hla, hlb, and coa) and virulence-regulated genes (RNAIII, agrA, and saeR). These results suggested that VraR might have a direct or indirect effect on virulence in S. aureus. In electrophoretic mobility shift assays, VraR did not bind to promoter sequences of hla, hlb, and coa genes, but it did bind to the agr promoter region. In DNase I footprinting assays, VraR protected a 15-nucleotide (nt) sequence in the intergenic region between the agr P2 and P3 promoters. These results indicated that when S. aureus is subject to induction by vancomycin, expression of vraR is upregulated, and VraR binding inhibits the function of the Agr quorum-sensing system, causing reductions in the virulence of VISA/hVISA strains. Our results suggested that VraR in S. aureus is involved not only in the regulation of vancomycin resistance but also in the regulation of virulence.

VraSR and Virulence Trait Modulation during Daptomycin Resistance in Methicillin-Resistant Staphylococcus aureus Infection

“…aureus virulence by binding the P2-P3 intergenic region of the agr promoter, indicating that when S. aureus is subject to vancomycin induction, VraR binds and inhibits the function of the Agr quorum sensing system, causing reductions in the virulence of VISA/hVISA strains (42, 43). Given our previous findings revealing (i) that VraSR is a key factor during DAP resistance and (ii) the defective expression of agr found in CB1634, we postulated that VraSR may transcriptionally regulate agr expression in CB1634.…”

Tuning of the Lethal Response to Multiple Stressors with a Single-Site Mutation during Clinical Infection by Staphylococcus aureus

“…agr -defective strains have been associated with the development of vancomycin tolerance ( 39 , 40 ); however, agr dysfunction is associated with only small reductions in killing that are apparent only with long-term, time-kill experiments ( 41 , 42 ). Consequently, we focused on several agents known to be rapid, concentration-dependent killers of S. aureus (gentamicin, ciprofloxacin, and daptomycin).…”

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

“…The acquisition of vancomycin resistance in S. aureus is often accompanied by reduced virulence. A recent study found that VraSR directly regulated the function of the Agr quorum-sensing system and, thus, inhibited virulence in S. aureus (53). However, our data showed that vraSR SS expression was significantly higher in vivo than in vitro, which prompted us to consider its potential roles in pathogenesis.…”