Variation in extracellular protease production among clinical isolates of Staphylococcus aureus due to different levels of expression of the protease repressor sarA.
Staphylococcus aureus produces four major extracellular proteases: staphylococcal serine protease (V8 protease; SspA), cysteine protease (SspB), metalloprotease (aureolysin; Aur), and staphopain (Scp). Several in vitro studies have suggested that these enzymes are important virulence factors. Here we analyzed the protease production of 92 S. aureus strains from infected human soft tissue. Twenty-one strains produced variable zones of proteolysis on casein agar plates, while the remaining 71 strains appeared to be protease negative. The major protease genes were present in all protease-positive (n = 5) and protease-negative (n = 12) strains analyzed. Northern blotting showed that transcription of the protease genes was suppressed due to increased sigma factor B (SigB)-dependent expression of the protease repressor SarA. Other SigB-dependent traits such as pigmentation and expression of asp 23 were also increased in protease-negative compared to protease-positive strains. Inactivation of sarA in three protease-negative strains resulted in increased transcription of all protease genes and increased protease production, while overexpression of sarA in a strain producing protease at high levels repressed protease production. Our results suggest that the protease genes are conserved among clinical S. aureus strains and that the level of SigB-dependent expression of the protease repressor sarA determines the level of protease production in each strain.
Microbiology and Tumor Biology Center (MTC), Karolinska Institutet, S-17177 Stockholm, Sweden. Anna.Karlsson@mtc.ki.se
Anna
A
Karlsson
Staffan
S
Arvidson
D001426:Bacterial Proteins / Q000235:genetics*; D003546:Cysteine Endopeptidases / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D008666:Metalloendopeptidases / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012697:Serine Endopeptidases / Q000235:genetics*; D013203:Staphylococcal Infections / Q000382:microbiology; D013211:Staphylococcus aureus / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification; D015534:Trans-Activators / Q000235:genetics*
C095698:Agr protein, Staphylococcus aureus; D001426:Bacterial Proteins; C088021:SarA protein, bacterial; D015534:Trans-Activators; D012697:Serine Endopeptidases; C028344:glutamyl endopeptidase; D003546:Cysteine Endopeptidases; D008666:Metalloendopeptidases; C115504:aureolysin