Understanding the specific molecular mechanisms that govern RNA mediated signaling in Staphylococcus aureus

Abstract

Staphylococcus aureus is a leading cause of both hospital and community associated infections. Antimicrobial resistance in S. aureus is brought about by diverse mechanisms. These include acquisition of mobile elements like pathogenicity islands (SaPIs), chromosome cassettes (SCC), transposons, conjugative plasmids and prophages contributing to the genome variation in different staphylococcal species. A distinctive feature of S. aureus is a phenotypic switch between a persistent and a virulent phenotype. The dormant cells (persister) arise at low cell density upon expression of protein factors and other adhesins promoting colonization and biofilm formation. At high cell density these bacteria initiate the secretion of a variety of toxins giving rise to virulent phenotype. This switch is considered to be a key factor in S. aureus pathogenesis. As in other bacteria, the quorum sensing mechanism plays a significant role in modulating bacterial infection. The dominant quorum sensing (QS) mechanism in S. aureus is the Accessory gene regulator (agr). The goal of the studies reported in this thesis was to understand the role played by signaling RNA, in particular RNAIII, in the phenotypic switch. We proposed to evaluate this mechanism in the context of a specific, characterized S. aureus strain. Towards this goal, we chose a specific S. aureus strain, LVP-7, from our in-house collection to initiate the study. The thesis thus has studies and analysis to understand the LVP-7 genotype and associated features, the expression profile and aspects that could help in delineating the role of the non-coding RNAIII from other sRNAs. Finally, we report the development of a fluorescence imaging assay to monitor the cellular level and, potentially, conformational features of RNAIII.