Subinhibitory concentrations of β-lactam induce haemolytic activity inStaphylococcus aureusthrough the SaeRS two-component system

Abstract

SaeRS is a two-component system that has been characterized as a positive regulatory system for the expression of several virulence factors, including coagulase, alpha-, beta- and gamma-haemolysins, nuclease, and fibronectin-binding proteins in Staphylococcus aureus. Previously, the SaeRS system was found to be induced at the transcriptional level by beta-lactam. Here, we found that subinhibitory concentrations of beta-lactam induce haemolytic activity in the S. aureus N315 strain but not in the saeRS null mutant KSA. Comparison of the transcriptional profile of the N315 and KSA strains by microarray analysis reveals that the SaeRS system modulates the regulation of coagulase (coa), alpha-, beta- and gamma-haemolysins (hla, hlb and hlg), nuclease (SA0746), fibrinogen-binding proteins (emp, efb, SA1000 and SA1004), fibronectin-binding protein B (fnbB), and 13 other genes. Further, the use of cefoxitin as a signal inducer reveals that the SaeRS system appears to modulate 22 additional genes as a secondary regulon, including the staphylococcal accessory regulators SarA and SarT and the Clp protease ATPase subunits ClpB and ClpL. These observations suggest that beta-lactam is able to induce the SaeRS system, which acts as a crucial signal transduction system for S. aureus pathogenicity rather than antimicrobial resistance.

The Virulence Regulator Sae ofStaphylococcus aureus:Promoter Activities and Response to Phagocytosis-Related Signals

“…However, at subinhibitory concentrations no effect was detectable. In summary, previous results from the literature concerning sae signaling could be confirmed with regard to the repression at low pH and high NaCl concentrations (33) and partly with regard to those concerning activation by vancomycin (25).…”

“…Subinhibitory concentrations of several classes of antibiotics have also been implicated in sae activation (glycopeptides, ␤-lactams) (25, 26) or inhibition (clindamycin) (33). The results on interactions with other virulence regulators such as agr and SigB are partially contradictory, which may be due to strain differences (15,25,33).We are able to show here that the sae upstream region contains two active promoter elements, P1 and P3. The main strongly autoregulated P1 promoter can be activated by H 2 O 2 and by subinhibitory concentrations of ␣-defensins, the key players in the phagocytic killing of bacteria.…”

“…Within this network sae appears to be a central downstream regulator that controls the expression of major virulence genes such as hla (coding for alpha-hemolysin), coa (coding for coagulase), or fnbA (coding for fibronectin-binding protein A) (11,33,39). Microarray analysis and proteomics have revealed that most of the genes activated by sae are involved in bacterial adhesion, immune modulation, or toxicity (25,29,38). In addition, the importance of gene regulation by sae in vivo was shown in several animal models (3,15,16,29,43).…”

“…The T1 transcript seems to be activated in the post-exponential-growth phase (33,39) but downregulated under low pH or osmotic upshift (33). Subinhibitory concentrations of several classes of antibiotics have also been implicated in sae activation (glycopeptides, ␤-lactams) (25,26) or inhibition (clindamycin) (33). The results on interactions with other virulence regulators such as agr and SigB are partially contradictory, which may be due to strain differences (15,25,33).…”

Identification of the P3 Promoter and Distinct Roles of the Two Promoters of the SaeRS Two-Component System in Staphylococcus aureus

“…P1 has also been reported to be affected by several environmental stressors. A high NaCl concentration and acidic conditions repress the promoter activity, while subinhibitory concentrations of beta-lactam antibiotics, hydrogen peroxide, or human neutrophil peptides activate it (12,22). Sometimes, these modulations of P1 activity were interpreted as a functional control of the SaeRS TCS.…”