Impact Of Ph-SA On The Activity Of Agr System In Staphylococcus Aureus

Staphylococcus aureus(SA), a significant human pathogen of nosocomial and community-acquired infection, has developed serious resistance to the most available antibiotics. The emergence of methicillin and vancomycin-resistant SA strains have brought enormous threat to the public health. Thus we have to develop novel antimicrobial agents for prevention and treament of antibiotic-resistant bacterial, especially staphylococcal infections.Pheromonicin-SA (Ph-SA is a peptide consisting of a staphylococcal AgrD 1 pheromone fused to the C-terminus of colicin Ia, a channel-forming bacteriocin had presented remarkable bactericidal activity against methicillin-resistant SA (MRSA). AgrD 1 targeted the channel-forming domain of colicin Ia to the cytoplasmic membrane of SA cells, then the channel-forming domain of colicin Ia inserted into the membrane to form the voltage-activated channel to kill the SA cells.The agr (accessory gene regulator) locus of SA cells is the substantial entity for the adjusting of virulence gene expression. It is a classical two-component quorum sensing regulatory system of prokaryotic cells.Based upon the structure of Ph-SA molecules, then, what kind of functional influence of Ph-SA should act on that agr system if the AgrD 1 epitope of Ph-SA molecules binding to the relative membrane agr receptors?In the present study, SA cells were divided into three groups, controK penicillin-treated and Ph-SA-treated. After SA cells growing in liquid medium about 3 hours, PBS, penicillin and Ph-SA were added into the medium respectively when the turbidity of medium reached 0.2(As95). Growing with agents for one hour, the supernant of medium were collected for the subsequent assays.The amount of delta-toxin from different groups and growth phases was measured by high performance liquid chromatography (HPLC). Influence of Ph-SA on SA exoprotein productions was shown by SDS-PAGE assay and the hemolytic activities of cultured filtrate on human erythrocytes were measured.Significantly, it was observed that the secretion of 5 -toxin in Ph-SA group was less than that of the other two groups at the same growth time(P<0.05), so were the production of exoproteins and proteins in cells in SDS-PAGE assay. These results indicated that Ph-SA molecules inhibited exoprotein production of tested S A cells. In addition the results of hemolytic activities on human erythrocytes were also supported our imaginationToxin production is the main pathogenicity of SA to the host. We suggested that Ph-SA could block the activity of agr system, acting as a pseudo-ligand, which can attenuate the virulence of SA via inhibition of exoprotein production.