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 α-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 α-toxin and protein A production. An inverse correlation between α-toxin and protein A production was found in most strains. The levels of α-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 α-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 α-toxin, OR153, although RNAIII is also strongly expressed, the specific hla mRNA was unexpectedly low. One partial explanation for the high α-toxin production by this clinical isolate might be its lack of extracellular proteases.
Published Version
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