| Staphylococcus aureus(S.aureus),an ubiquitous opportunistic pathogen in nature,has been a serious threat to public health with persistent colonization of approximately 20% of the human population.This gram positive bacterium can lead to both superficial infections including skin and soft-tissue infections,and invasive and life-threatening infectious diseases with significant mortality,such as necrotizing pneumonia,bacteremia and sepsis.However,due to this bacteria's remarkable ability to acquire resistance to various antibiotics,numerous lineages of methicilin-resistant Staphylococcus aureus(MRSA)have been isolated clinically,and among the prevalent MRSA strains,the most widely studied and widely existing strain is USA300.Antibiotic therapies using vancoycin,linezolid and daptomycin were considered as the mainstay against MRSA infection.However,MRSA resistance to those antibiotics has been described in clinical settings,further worsening this situation.Meanwhile,the unsuccessful practices of antibiotic therapies have been increasingly reported.The inevitability of S.aureus resistance to commonly prescribed antibiotics coupled with the relatively lagging development of new antibiotics cry for alternatives to traditional antibiotic therapies.S.aureus is a well-armed pathogen that can produce a broad range of virulence factors which are essential for adhesion,invasion,immune evasion and cell damage,such as sortase,adhesins,?-toxin,Panton-Valentine leukokcidin(PVL),etc.Among these virulence factors,sortase mediated the anchorage for surface proteins is critical for the adesion of bacterial infection.Additiaonlly,?-toxin is a versatile water-soluble virulence factor that plays an important role in skin and soft tissue infections,necrotizing pneumonia and fatal sepsis.Several studies have demonstrated that ?-toxin or sortase mutants displayed less virulence in animal models of pneumonia,dermonecrotic skin infection,sepsis,peritonitis,and infection of cornea,central nervous system,endocardium,nephritis and mammary gland.The essential role of ?-toxin and sortase in the pathogenicity of S.aureus infection suggests that targeting these virulence factors would be a promising strategy for the discovery of anti-virulence agents against USA300 infection.Dracorhodin perochlorate(DP),a natural compound isolated from the fruit named Daemonorops draco,has been demonstrated to be capable of inducing apoptosis in Hela cells and human breast cancer MCF-7 cells.In the present work,DP was identified as an effective inhibitor of ?-toxin using hemolysis assay.The coculture of DP with S.aureus significantly inhibited the hemolytic activity of bacterial supernatants.Furthermore,the production of ?-toxin into bacterial culture supernatants was remarkably decreased in the presence of DP,suggesting that the attenuation of supernatants hemolysis was due to inhibition of ?-toxin production by DP.Using RT-PCR assay,we discovered that DP,at final concentration of 16 ?g/ml,significantly inhibited ?-toxin expression by down-regulating the transciption of hla and RNAIII.In addition,the addition of DP could effectively protect A549 and MH-S from cell injury induced by S.aureus.In addition,DP treatment significantly attenuated the activity of sortase and subsequently,inhibited the adhesion and invasion of S.aureus.Computational biology and site directed mutagenesis verified the binding of DP with sortase via P30 and T105 residues occupied the active center of sortase and neutralized its activity.Furthermore,the treatment with DP significantly decreased the mortality of S.aureus infected mice and,also,attenuated the pathological damage of lungs of S.aureus infected mice.Our results may offer a new agent and novel strategy for the development of anti-virulence agents against S.aureus,especially MRSA infection. |
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