cis- and trans-acting Transcriptional Activators: Characterization of Single Nucleotide Polymorphisms and a Novel Two-component System of Staphylococcus aureus

Staphylococcus aureus is a major opportunistic pathogen and a common cause of hospital- and community-acquired infections. Furthermore, infections of livestock animals by S. aureus results in billion dollar losses to agriculture producers annually. Over the last five decades antibiotic resistance has dramatically increased in S. aureus and highly pathogenic strains have emerged that threaten human and animal health. Characterization of highly pathogenic strains and novel transcriptional mechanisms and pathways is of utmost importance as it will provide a critical evolutionary understanding of the transcriptional changes that led to the emergence of successfully infectious S. aureus strains and may identify novel targets for antibacterial development.;The overarching goal of research described in this thesis was to characterize and understand how novel cis - and trans-acting factors affect gene expression in S. aureus. To that end, the work and data presented investigate the effect of promoter based single nucleotide polymorphisms (SNPs) of the hla gene, encoding &agr;-toxin, on gene transcription and gene product expression. The cis-acting SNPs increased the binding affinity of the promoter to the trans-acting transcription factor SarZ. Furthermore, the S. aureus RF122 strain had increased transcriptional expression of several positive regulators and decreased transcription of negative regulators of hla, which resulted in a dramatic increase in alpha-toxin expression and likely contributes to the increased mastitis pathogenesis of RF122.;Additionally, the essentiality of the yhcSR two-component system was confirmed in the hospital-acquired methicillin resistant S. aureus WCUH29 strain. The YhcSR TCS was identified to transcriptionally activate the lacABCDE and opuCABC operons involved in cellular metabolism and osmoregulatory mechanisms, respectively. In an effort determine if a relationship existed between YhcSR and pathogenesis, studies revealed that the YhcSR TCS transcriptionally regulated, in a positive manner, the sspABC and crtOPQMN operons, encoding exported proteases and staphyloxanthin biosynthesis, which contribute to the survival of S. aureus in human blood. The data indicate that the YhcSR TCS system is an essential trans-acting global regulator in S. aureus..