The role of environmental factors in the regulation of virulence-determinant expression in Staphylococcus aureus 8325-4

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Abstract
Staphylococcus aureusis a major human pathogen, which produces a variety of virulence determinants. To study environmental regulation of virulence-determinant production, several transcriptional reporter gene fusions were constructed. 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. The effect of many different environmental conditions on the expression of the fusions was examined. Expression ofhla, tstandspawas strongly repressed in the presence of sodium chloride (1 M) or sucrose (20 mM), butsarAwas relatively unaffected. The global regulator of expression of virulence-determinant genes,agr(accessory gene regulator) was not involved in the salt or sucrose repression. Novobiocin, a DNA gyrase inhibitor, did not significantly increase the expression oftstin wild-type oragrbackgrounds and failed to relieve the salt suppression. Expression oftstwas strongly stimulated in several low-metal environments, independently ofagr,whilstspalevels were significantly reduced by EGTA. The complex, interactive role of environmental factors in the control of expression of the virulence determinants is discussed.