SarS Is a Repressor of Staphylococcus aureus Bicomponent Pore-Forming Leukocidins

The ability of sarA to limit protease production plays a key role in the pathogenesis of Staphylococcus aureus osteomyelitis irrespective of the functional status of agr

We demonstrate that mutation of the staphylococcal accessory regulator A (sarA) in the USA300 strain LAC limits virulence in a murine osteomyelitis model to a greater extent than mutation of the accessory gene regulator (agr) and that it does so irrespective of the functional status of agr. Protease production was decreased in the agr mutant but increased in sarA and sarA/agr mutants to a degree that limited biofilm formation. Extracellular protein A (eSpa) and full-length extracellular nuclease (Nuc1) were absent in the conditioned medium (CM) from sarA and sarA/agr mutants, and their abundance was restored in both mutants by eliminating protease production. Cytotoxicity of CM for osteoblasts and osteoclasts was also reduced in both mutants. Cytotoxicity was restored in a protease-deficient sarA mutant but not in the protease-deficient sarA/agr mutant. Reduced cytotoxicity was correlated with the reduced abundance of full-length α-toxin, LukF, and LukS in sarA and sarA/agr mutants. The abundance of these toxins in their full-length form was increased in the protease-deficient sarA mutant by comparison to LAC, demonstrating that mutation of sarA increases the production of these toxins but increased protease production limits their abundance in full-length and presumably functional forms. Most importantly, eliminating protease production enhanced the virulence of sarA and sarA/agr mutants, but had no impact in the agr mutant. We conclude that a key factor in the attenuation of LAC sarA and sarA/agr mutants in osteomyelitis is the increased production of extracellular proteases and its impact on virulence factors that contribute to biofilm formation and cytotoxicity.IMPORTANCEThe persistent emergence of antibiotic-resistant strains has rekindled interest in anti-virulence strategies to combat S. aureus infections. Numerous reports describe anti-virulence strategies focusing on key regulatory elements that globally influence virulence factor production, the two most commonly targeted being the accessory gene regulator (agr) and the staphylococcal accessory regulator A (sarA). We demonstrate that mutation of sarA limits virulence to a greater extent than mutation of agr and that this can be attributed to increased protease production in both sarA and sarA/agr mutants. This illustrates the critical role of sarA in protease-mediated post-translational regulation in S. aureus. It also suggests that an inhibitor of sarA would be more effective than an inhibitor of agr in overcoming the therapeutic recalcitrance of osteomyelitis and that such an inhibitor would remain effective even in the context of agr mutants known to arise in vivo during the transition from acute to chronic infection.

Lysine succinylome analysis of MRSA reveals critical roles in energy metabolism and virulence

Methicillin-resistant Staphylococcus aureus's (MRSA) resistance poses a global health challenge. This study investigates lysine succinylation in MRSA using proteomics and bioinformatics approaches to uncover metabolic and virulence mechanisms, with the goal of identifying novel therapeutic targets. Mass spectrometry and bioinformatics analyses mapped the MRSA succinylome, identifying 8048 succinylation sites on 1210 proteins. These analyses included Gene Ontology annotation, Kyoto Encyclopedia of Genes and Genomes pathway enrichment, and protein-protein interaction (PPI) network construction (e.g. using the STRING database, a widely used online tool for analyzing protein-protein interactions), providing a comprehensive functional and interactive landscape of succinylated proteins. The succinylated proteins were predominantly involved in cytoplasmic metabolic processes, with enrichment in glycolysis/gluconeogenesis and the tricarboxylic acid cycle. Both of these pathways are critical for MRSA's energy production, growth, and virulence, supplying the necessary metabolic intermediates and energy to support bacterial survival and pathogenicity. Motif analysis revealed 13 conserved motifs, while PPI analysis highlighted fibronectin-binding protein A (FnbA) as a central virulence factor. Succinylation significantly influences MRSA's metabolism and virulence, potentially impacting biofilm by modifying key proteins such as FnbA, bifunctional autolysin, and S-ribosylhomocysteine lyase(LuxS). These findings provide new avenues for developing antibiofilm strategies and therapeutic interventions against MRSA.

Isolation and characterization of persisters of the pathogenic microorganism Staphylococcus aureus

The presence of antibiotic persisters is one of the leading causes of recurrent and chronic diseases. One challenge in mechanistic research on persisters is the enrichment of pure persisters. In this work, we validated a proposed method to isolate persisters with notorious Staphylococcus aureus cultures. With this, we analyzed the proteome profile of pure persisters and revealed the distinct mechanisms associated with vancomycin and enrofloxacin induced persisters. Furthermore, morphological and metabolic characterizations were performed, indicating further differences between these two persister populations. Finally, we assessed the effect of ATP repression, protein synthesis inhibition, and reactive oxygen species (ROS) level on persister formation. In conclusion, this work provides a comprehensive understanding of S. aureus vancomycin and enrofloxacin induced persisters, facilitating a better mechanistic understanding of persisters and the development of effective strategies to combat them.

Prophage-encoded methyltransferase drives adaptation of community-acquired methicillin-resistant Staphylococcus aureus

We recently described the evolution of a community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) USA300 variant responsible for an outbreak of skin and soft tissue infections. Acquisition of a mosaic version of the Φ11 prophage (mΦ11) that increases skin abscess size was an early step in CA-MRSA adaptation that primed the successful spread of the clone. The present report shows how prophage mΦ11 exerts its effect on virulence for skin infection without encoding a known toxin or fitness genes. Abscess size and skin inflammation were associated with DNA methylase activity of an mΦ11-encoded adenine methyltransferase (designated pamA). pamA increased expression of fibronectin-binding protein A (fnbA; FnBPA), and inactivation of fnbA eliminated the effect of pamA on abscess virulence without affecting strains lacking pamA. Thus, fnbA is a pamA-specific virulence factor. Mechanistically, pamA was shown to promote biofilm formation in vivo in skin abscesses, a phenotype linked to FnBPA's role in biofilm formation. Collectively, these data reveal a novel mechanism-epigenetic regulation of staphylococcal gene expression-by which phage can regulate virulence to drive adaptive leaps by S. aureus.

Staphylococcus aureus senses human neutrophils via PerR to coordinate the expression of the toxin LukAB

Staphylococcus aureus is a gram-positive pathogen that poses a major health concern, in part due to its large array of virulence factors that allow infection and evasion of the immune system. One of these virulence factors is the bicomponent pore-forming leukocidin LukAB. The regulation of lukAB expression is not completely understood, especially in the presence of immune cells such as human polymorphonuclear neutrophils (hPMNs). Here, we screened for transcriptional regulators of lukAB during the infection of primary hPMNs. We uncovered that PerR, a peroxide sensor, is vital for hPMN-mediated induction of lukAB and that PerR upregulates cytotoxicity during the infection of hPMNs. Exposure of S. aureus to hydrogen peroxide (H2O2) alone also results in increased lukAB promoter activity, a phenotype dependent on PerR. Collectively, our data suggest that S. aureus uses PerR to sense the H2O2 produced by hPMNs to stimulate the expression of lukAB, allowing the bacteria to withstand these critical innate immune cells.IMPORTANCEStaphylococcus aureus utilizes a diverse set of virulence factors, such as leukocidins, to subvert human neutrophils, but how these toxins are regulated is incompletely defined. Here, we identified the peroxide-sensitive repressor, PerR, as a required protein involved in the induction of lukAB in the presence of primary human neutrophils, a phenotype directly linked to the ability of PerR to sense H2O2. Thus, we show that S. aureus coordinates sensing and resistance to oxidative stress with toxin production to promote pathogen survival.

SarS and Rot are necessary for the repression of lukED and lukSF-PV in Staphylococcus aureus

IMPORTANCE

The leukocidins play an important role in disarming the host immune system and promoting infection. While both SarS and Rot have been established as repressors of leukocidins, the importance of each repressor in infection is unclear. Here, we demonstrate that repression by SarS and Rot is not additive and show that in addition to upregulating expression of each other, they are also able to bind concurrently to the leukocidin promoters. These findings suggest that both repressors are necessary for maximal repression of lukED and lukSF-PV and illuminate another complex relationship among Staphylococcus aureus virulence regulators.