Role of the msaABCR Operon in Cell Wall Biosynthesis, Autolysis, Integrity, and Antibiotic Resistance in Staphylococcus aureus

Abstract

Staphylococcus aureus is an important human pathogen in both community and health care settings. One of the challenges with S. aureus as a pathogen is its acquisition of antibiotic resistance. Previously, we showed that deletion of the msaABCR operon reduces cell wall thickness, resulting in decreased resistance to vancomycin in vancomycin-intermediate S. aureus (VISA). In this study, we investigated the nature of the cell wall defect in the msaABCR operon mutant in the Mu50 (VISA) and USA300 LAC methicillin-resistant Staphylococcus aureus (MRSA) strains. Results showed that msaABCR mutant cells had decreased cross-linking in both strains. This defect is typically due to increased murein hydrolase activity and/or nonspecific processing of murein hydrolases mediated by increased protease activity in mutant cells. The defect was enhanced by a decrease in teichoic acid content in the msaABCR mutant. Therefore, we propose that deletion of the msaABCR operon results in decreased peptidoglycan cross-linking, leading to increased susceptibility toward cell wall-targeting antibiotics, such as β-lactams and vancomycin. Moreover, we also observed significantly downregulated transcription of early cell wall-synthesizing genes, supporting the finding that msaABCR mutant cells have decreased peptidoglycan synthesis. More specifically, the msaABCR mutant in the USA300 LAC strain (MRSA) showed significantly reduced expression of the murA gene, whereas the msaABCR mutant in the Mu50 strain (VISA) showed significantly reduced expression of glmU, murA, and murD. Thus, we conclude that the msaABCR operon controls the balance between cell wall synthesis and cell wall hydrolysis, which is required for maintaining a robust cell wall and acquiring resistance to cell wall-targeting antibiotics, such as vancomycin and the β-lactams.

VraCP regulates cell wall metabolism and antibiotic resistance in vancomycin-intermediateStaphylococcus aureusstrain Mu50

“… 14 Any compromise of the cell wall plays an integral part in antibiotic resistance, because it is targeted by many antibiotics, including β-lactams (oxacillin), glycopeptides (vancomycin and teicoplanin) and other cell wall-associated antibiotics (daptomycin). 15 , 16 Vancomycin interferes with late-stage peptidoglycan synthesis by forming non-covalent hydrogen bonds with the penultimate d -Ala- d -Ala residues of newly synthesized UDP-MurNAc-pentapeptides, thereby disrupting downstream peptidoglycan assembly, cell wall synthesis is ultimately inhibited. 17 VISA strains share some common characteristics, including thickened cell wall, decreased autolytic activity, reduced cross-linking of peptidoglycan, slower growth rate and attenuated virulence.…”

Staphylococcus aureus Synergized with Candida albicans to Increase the Pathogenesis and Drug Resistance in Cutaneous Abscess and Peritonitis Murine Models

“…Most drugs used for controlling S. aureus -related infections target cell wall biosynthesis, and increased peptidoglycan cross-linking is believed to contribute to the acquirement of drug-resistant capability. It has been observed that decreased peptidoglycan cross-linking leads to increased susceptibility toward cell-wall-targeting antibiotics, namely β-lactams and vancomycin [ 48 , 49 ]. Our transcriptome results, suggesting the over-expression of cell wall biosynthetic pathways, including penicillin-binding proteins, imply another way for the up-regulation of antibiotic resistance in S. aureus and C. albicans dual-species biofilms ( Figure 4 a,b and Figure S2 ).…”

Comparative proteomic analysis of vancomycin-sensitive and vancomycin-intermediate resistant S. aureus

“…MurA (UDP-N-acetylglucosamine 1-carboxyvinyltransferase), in the first committed step of peptidoglycan biosynthesis, catalyzes the transfer of enolpyruvate from phosphoenolpyruvate to UDP-NAG, releasing inorganic phosphate[35]. The deletion/inactivation of murA gene from S. aureus and Streptococcus pneumoniae has been reported to be lethal for bacteria due to the loss of cell integrity and susceptibility to osmotic lysis[36]. The importance of MurA as a drug target is also substantiated by the fact that the antibacterial activity of an antibiotic, fosfomycin is due to its covalent binding to the active site of MurA enzyme [37, 38].…”