Transcription profiling-based identification of Staphylococcus aureus genes regulated by the agr and/or sarA loci

The advent of transcription profiling technologies has provided researchers with an unprecedented ability to study biological processes. Accordingly, a custom-made Affymetrix GeneChip, constituting > 86% of the Staphylococcus aureus genome, was used to identify open reading frames that are regulated by agr and/or SarA, the two best-studied regulators of the organism's viru lence response. RNA extracted from wild-type cells and agr, sarA, and agr s arA mutant cells in the early-, mid-, and late-log and stationary phases of growth was analyzed. Open reading frames with transcription patterns expec ted of genes either up- or downregulated in an agr- and/or SarA-dependent m anner were identified. Oligonucleotide microarray and Northern blot analyse s confirmed that the transcription of several known virulence genes, includ ing hla (alpha-toxin) and spa (protein A), is regulated by each effector an d provided insights about the regulatory cascades involved in both alpha-he molysin and protein A expression. Several putative virulence factors were a lso identified as regulated by agr and/or SarA. In addition, genes that are involved in several biological processes but which are difficult to reconc ile as playing a direct role in the organism's pathogenesis also appeared t o be regulated by each effector, suggesting that products of both the agr a nd the sarA locus are more-global transcription regulators than previously realized.