The Impacts of msaABCR on sarA -Associated Phenotypes Are Different in Divergent Clinical Isolates of Staphylococcus aureus

Abstract

The staphylococcal accessory regulator (sarA) plays an important role in Staphylococcus aureus infections, including osteomyelitis, and the msaABCR operon has been implicated as an important factor in modulating expression of sarA. Thus, we investigated the contribution of msaABCR to sarA-associated phenotypes in the S. aureus clinical isolates LAC and UAMS-1. Mutation of msaABCR resulted in reduced production of SarA and a reduced capacity to form a biofilm in both strains. Biofilm formation was enhanced in a LAC msa mutant by restoring the production of SarA, but this was not true in a UAMS-1 msa mutant. Similarly, extracellular protease production was increased in a LAC msa mutant but not a UAMS-1 msa mutant. This difference was reflected in the accumulation and distribution of secreted virulence factors and in the impact of extracellular proteases on biofilm formation in a LAC msa mutant. Most importantly, it was reflected in the relative impact of mutating msa as assessed in a murine osteomyelitis model, which had a significant impact in LAC but not in UAMS-1. In contrast, mutation of sarA had a greater impact on all of these in vitro and in vivo phenotypes than mutation of msaABCR, and it did so in both LAC and UAMS-1. These results suggest that, at least in osteomyelitis, it would be therapeutically preferable to target sarA rather than msaABCR to achieve the desired clinical result, particularly in the context of divergent clinical isolates of S. aureus.

SarA plays a predominant role in controlling the production of extracellular proteases in the diverse clinical isolates ofStaphylococcus aureusLAC and UAMS-1

“…fluorescence was significantly higher in the sarA mutants with all four reporters including the spl::gfp reporter, and this was true in both LAC and UAMS-1 (Rom et al, 2020). This confirms that SarA represses expression of all four of the transcriptional units encoding aureolysin, ScpA, SspA/SspB, and SplA-F, and the results of our binding assays suggest that it does so by directly binding to cis elements associated with all four of the relevant promoter regions.…”

“…Changes in the production of extracellular proteases have been correlated with clinically-relevant phenotypes of S. aureus including the accumulation of alpha toxin and protein A, biofilm formation, and virulence in diverse animal models (Beenken et al, 2010, Kolar et al, 2013, Loughran et al, 2014, Mootz et al, 2015, Rom et al, 2017, Rom et al, 2020, Trotonda et al, 2008, Tsang et al, 2008. Indeed, eliminating the production of aureolysin, SspA, SspB, ScpA, and the SplA-F proteases, or increasing the production of these same proteases, has been shown to have a dramatic impact on virulence and the overall S. aureus virulence factor repertoire (Byrum et al, 2018a, Kolar et al, 2013.…”

“…Fluorescence was assessed as previously described (Rom et al, 2020). Briefly, ON cultures were standardized by optical density.…”

The role of the msaABCR operon in implant-associated chronic osteomyelitis in Staphylococcus aureus USA300 LAC

“…In this study, msaABCR whole cell proteomics analysis also showed significant production of SspA, SspB, SspC, Aur, and staphopain A. A study by Rom JS et al, [ 84 ] showed reduced accumulation of alpha toxin (Hla) and extracellular protein A in the msaABCR mutant [ 84 ]. They also showed that deletion of msaABCR leads to the significant decrease in accumulation of extracellular proteins [ 84 ].…”

“…Several staphylococcal virulence factors that are cytotoxic to osteoblasts, triggers osteoclastogenesis, and induces bone loss and/or destruction are also affected in the msaABCR mutant (Table 2 ). Several previous studies have linked increased protease production with defective biofilm formation, reduced accumulation of secreted virulence factors, reduced toxicity to osteoblasts and osteoclasts cells in vitro, and reduced virulence and attenuation in OM infection [ 31 , 46 , 51 – 53 , 73 , 84 ]. Cassat et al 2013 [ 46 ] showed that extracellular-secreted proteases, mainly aureolysin (Aur), significantly reduced the abundance of staphylococcal exoproteomes that are important for host-tissue binding, biofilm formation, invasion of host cells, and the cytolytic factors that trigger cortical bone destruction.…”