title: Variation in the agr-dependent expression of alpha-toxin and protein A among clinical isolates of Staphylococcus aureus from patients with septicaemia.
abstract: In Staphylococcus aureus synthesis of many virulence factors is regulated by the agr locus. The regulatory molecule RNAIII, induced by agr, activates transcription of the alpha-toxin gene, hla, while it acts as a repressor of the protein A gene, spa. Forty clinical strains of S. aureus from human blood cultures were analysed for alpha-toxin and protein A production. An inverse correlation between alpha-toxin and protein A production was found in most strains. The levels of alpha-toxin and protein A production varied significantly among strains, which indicates various levels of the regulator, RNAIII. This was confirmed by selecting strains producing different amounts of alpha-toxin, showing that the variations in toxin production are due to the variations of RNAIII transcript. However, in one of the selected strains which produced high levels of alpha-toxin, OR153, although RNAIII is also strongly expressed, the specific hla mRNA was unexpectedly low. One partial explanation for the high alpha-toxin production by this clinical isolate might be its lack of extracellular proteases.
authors.affiliation: Microbiology and Tumorbiology Center, Karolinska Institute, Stockholm, Sweden.
authors.forename: S
authors.initials: S
authors.lastname: Li
authors.forename: S
authors.initials: S
authors.lastname: Arvidson
authors.forename: R
authors.initials: R
authors.lastname: Möllby
mesh_terms: D016470:Bacteremia / Q000382:microbiology*; D001426:Bacterial Proteins / Q000235:genetics*; D001427:Bacterial Toxins / Q000096:biosynthesis*; D006460:Hemolysin Proteins / Q000096:biosynthesis*; D006801:Humans; D016372:RNA, Antisense / Q000502:physiology; D012329:RNA, Bacterial / Q000502:physiology; D013205:Staphylococcal Protein A / Q000096:biosynthesis*; D013211:Staphylococcus aureus / Q000378:metabolism*; D015534:Trans-Activators; D014157:Transcription Factors / Q000235:genetics*
chemical_list: C095698:Agr protein, Staphylococcus aureus; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D006460:Hemolysin Proteins; D016372:RNA, Antisense; D012329:RNA, Bacterial; C096035:RNAIII, Staphylococcus aureus; D013205:Staphylococcal Protein A; D015534:Trans-Activators; D014157:Transcription Factors; C021091:staphylococcal alpha-toxin