Staphylococcus aureus svrA: a gene required for virulence and expression of the agr locus c cThe GenBank accession numbers for the svrA gene are SAV0334 (S. aureus subsp. aureus Mu50) and SA0323 (S. aureus subsp. aureus N315).

Abstract

A Staphylococcus aureus gene originally identified by signature-tagged mutagenesis as being required for virulence was cloned, sequenced and named svrA. Hydropathy profiles revealed that SvrA is likely to be membrane associated, having two regions with six membrane-spanning domains, the regions separated by an extended hydrophilic loop. When compared with the wild-type strain, an svrA mutant expressed greatly reduced amounts of α-, β-and δ-toxins and an increased amount of protein A. Toxin production by the mutant strain was restored to wild-type levels when complemented with a plasmid expressing the svrA gene. Northern hybridization with probes specific for hla (encoding α-toxin) and spa (encoding protein A) showed that the svrA mutant strain was affected in the transcription of these genes. svrA mRNA was present in wild-type and agr strains, but agr mRNA and RNAIII were absent in the svrA mutant strain. Virulence studies suggested that the attenuation of the svrA mutant was probably due to its direct or indirect effect on the agr regulon. These results indicate that svrA is required for the expression of agr and RNAIII transcripts and is therefore a new component of the agr regulatory network controlling virulence gene expression in S. aureus.

DEAD-Box RNA Helicases in Gram-Positive RNA Decay

“…Hemolysin alpha is highly active against rabbit blood, whereas horse erythrocytes are highly vulnerable to hemolysin delta (note: hemolysin beta can be assayed using sheep blood; Garvis et al, 2002).…”

“…The easiest way of testing hemolysis activity is via blood-agar plates, which will give a semiquantitative estimate of activity (Garvis et al, 2002). Rich medium (e.g., Mueller-Hinton, Becton Dickinson, NJ, USA), autoclaved with 10 g/l agar, is cooled to 43 C and mixed with 7% defibrinated blood, preheated to 43 C (TCS Biosciences Ltd., Buckingham, UK), whereupon the mix is immediately poured into petri dishes (antibiotics can be added if desired).…”

svrA, a multi-drug exporter, does not control agr

“…Consistent with this phenotype, agr transcripts are undetectable in the svrA mutant. These results suggest that svrA is a required upstream activator of agr, and that the lack of agr expression is responsible for the observed attenuation of virulence (Garvis et al, 2002).…”

“…Characterization of the svrA phenotype Strain P6C63 was recovered as a Tn917 insertion mutant that was attenuated for mouse virulence and found to have a profound defect in agr expression, both of which were complemented by an svrA clone (Garvis et al, 2002). We readily confirmed the agr-expression defect, but because of the well-known genotypic instability of the agr locus (Bjorklind & Arvidson, 1980;Somerville et al, 2002; R. P. Novick and others, unpublished results), we felt it necessary to confirm the reported linkage of the transposon to the agrdefective phenotype.…”

“…Subsequent analysis of the svrA mutant, strain P6C63, has revealed an approximately 10 3 -fold attenuation in virulence coupled with a phenotype typical of a strain that does not express agr (Garvis et al, 2002). Such strains fail to produce many of the typical staphylococcal exoproteins, including a-and d-toxins, and produce reduced amounts of b-toxin in comparison with typical agr + strains.…”