Molecular Basis of Resistance to Muramidase and Cationic Antimicrobial Peptide Activity of Lysozyme in Staphylococci

Abstract

It has been shown recently that modification of peptidoglycan by O-acetylation renders pathogenic staphylococci resistant to the muramidase activity of lysozyme. Here, we show that a Staphylococcus aureus double mutant defective in O-acetyltransferase A (OatA), and the glycopeptide resistance-associated two-component system, GraRS, is much more sensitive to lysozyme than S. aureus with the oatA mutation alone. The graRS single mutant was resistant to the muramidase activity of lysozyme, but was sensitive to cationic antimicrobial peptides (CAMPs) such as the human lysozyme-derived peptide 107R-A-W-V-A-W-R-N-R115 (LP9), polymyxin B, or gallidermin. A comparative transcriptome analysis of wild type and the graRS mutant revealed that GraRS controls 248 genes. It up-regulates global regulators (rot, sarS, or mgrA), various colonization factors, and exotoxin-encoding genes, as well as the ica and dlt operons. A pronounced decrease in the expression of the latter two operons explains why the graRS mutant is also biofilm-negative. The decrease of the dlt transcript in the graRS mutant correlates with a 46.7% decrease in the content of esterified d-alanyl groups in teichoic acids. The oatA/dltA double mutant showed the highest sensitivity to lysozyme; this mutant completely lacks teichoic acid–bound d-alanine esters, which are responsible for the increased susceptibility to CAMPs and peptidoglycan O-acetylation. Our results demonstrate that resistance to lysozyme can be dissected into genes mediating resistance to its muramidase activity (oatA) and genes mediating resistance to CAMPs (graRS and dlt). The two lysozyme activities act synergistically, as the oatA/dltA or oatA/graRS double mutants are much more susceptible to lysozyme than each of the single mutants.

Differential regulation of staphylococcal virulence by the sensor kinase SaeS in response to neutrophil-derived stimuli

“…As a control, the expression profile of dltA was assessed to ensure the SaeS point mutations were not causing any changes in gene expression unrelated to the sae system (Fig. 6D) (37). Results for α-defensin-induced gene expression followed the same trends as the PMN results with the exception of hlgA in F33A, which had a robust response to PMNs and a diminished response to α-defensin (Fig.…”

Dual Targeting of Cell Wall Precursors by Teixobactin Leads to Cell Lysis

“…GraRS is a well-studied system which regulates the resistance to cationic antimicrobial peptides. A ⌬graRS mutant displays reduced expression of atl (41). These findings suggest that atl transcription is inactivated via WalKR and/or GraRS systems under cell wall stress conditions.…”

Regulation of bacterial virulence gene expression by cell envelope stress responses

“…142 Other S. aureus microarray analyses have expanded the influence of GraXSR to the differential expression of 248 genes in one case and 424 in another. 180,181 Among the most highly upregulated were those encoding virulence factors. For example, the agrBDCA operon, encoding a virulenceregulating quorum-sensing system, was expressed up to 21-fold higher in graSR C vs. DgraSR cells grown with colistin.…”