Abstract
ABSTRACT Methicillin-resistant Staphylococcus aureus (MRSA), also known as oxacillin-resistant S. aureus, is a leading cause of community and hospital associated infections globally. In this work, we found that deletion of the arlRS two-component system genes in the USA300 and USA500 strains resulted in increased susceptibilities to oxacillin (8–16-fold decrease in minimal inhibitory concentrations). In USA300ΔarlRS, transcriptional levels of mecA or blaZ showed no obvious change, while mRNA levels of spx showed a 4-fold decrease at 4 h and a 6.3-fold decrease at 10 h. Overexpression of spx in ΔarlRS restored oxacillin resistance to a similar level in USA300. In addition, gel shift assay showed that the recombinant ArlR bound to spx promoter region. Furthermore, silencing of spx led to a significant increase of oxacillin susceptibility in multiple MRSA isolates. Our results indicate that ArlRS plays a strong role in regulating oxacillin resistance in MRSA strains, which involves direct modulation of spx expression. Moreover, oritavancin showed inhibition to ATPase activity of the recombinant histidine kinase ArlS (IC50 = 5.47 μM). Oritavancin had synergy effect on oxacillin activity against the MRSA strains in both planktonic and biofilm state. Our data suggest that ArlRS is an attractive target for breaking antimicrobial resistance of MRSA.
Highlights
Staphylococcus aureus is a major pathogen causing both community-acquired and hospital-acquired infections globally [1]
To investigate the effect of ArlRS two-component system on oxacillin resistance in Methicillin-resistant Staphylococcus aureus (MRSA), an arlRS genes knockout mutant strain was constructed by homologous recombination using USA300 TCH1516 (GenBank Accession Number: NC_010079) as a parent strain, designated USA300ΔarlRS
We find that the two-component signal transduction system ArlRS regulates susceptibility to oxacillin in MRSA strains USA300, USA500 as well as three clinical isolates
Summary
Staphylococcus aureus is a major pathogen causing both community-acquired and hospital-acquired infections globally [1]. Oxacillin is a β-lactam antibiotic targeting penicillinbinding protein 2 (PBP2). Most MRSA strains possess a mecA gene that encodes an alternative form of PBP2 called PBP2a (or PBP2′). PBP2a can take over the transpeptidation function of PBP2, but it has a lower penicillinbinding affinity and is resistant to the action of oxacillin [6]. PBP2a synthesis is modulated by the transcriptional regulator MecI and the signal transduction protein MecR1, which are encoded by mecI and mecR1 genes located adjacent to mecA on the staphylococcal chromosome [7,8]. MecI and MecR1 share high protein sequence similarity with BlaI and BlaR1 [9], respectively, which may have the function of regulating PBP2a expression. In many clinical isolates of MRSA, a plasmid carrying blaI and blaR1 genes can encode proteins modulating PBP2a expression [10,11].
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