Expression of tst was strongly stimulated in several low-metal environments, independently of agr, whilst spa levels were significantly reduced by EGTA. Novobiocin, a DNA gyrase inhibitor, did not significantly increase the expression of tst in wild-type or agr backgrounds and failed to relieve the salt suppression. The global regulator of expression of virulence-determinant genes, agr (accessory gene regulator) was not involved in the salt or sucrose repression. Expression of hla, tst and spa was strongly repressed in the presence of sodium chloride (1 M) or sucrose (20 mM), but sarA was relatively unaffected. The effect of many different environmental conditions on the expression of the fusions was examined. Chromosomal fusions were made with the staphylococcal accessory regulator (sarA), α-haemolysin (hla), surface protein A (spa) and toxic-shock syndrome toxin-1 (tst) genes. To study environmental regulation of virulence-determinant production, several transcriptional reporter gene fusions were constructed. Staphylococcus aureus is a major human pathogen, which produces a variety of virulence determinants.
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