Peptidoglycome of gram-positive bacteria.

Our modern healthcare system faces imminent threats from multidrug-resistant pathogens due to their unprecedented increase in the frequency of infections in clinical environment compounded by the lack of novel antibiotic development. One of the leading targets for the development of novel antimicrobial agents is the bacterial cell wall. The cell wall is a unique feature found in all eubacteria with peptidoglycan (PG) as its primary component. PG plays a crucial role in protecting the bacteria from fluctuating osmotic pressures and the external environment. Thus, chemotherapeutic agents that interfere with PG biosynthesis or target its assembly can potentially lead to the development of novel antibiotics. To facilitate the understanding of how bacteria become resistant to antibiotics and the development of new-generation cell-wall targeting antimicrobial agents, our research focuses on the comprehensive in-depth study of PG composition analysis of clinically important Gram-positive pathogens (Enterococcus faecalis and Mycobacterium species) through liquid chromatography/mass spectrometry (LC/MS). This dissertation provides an innovative approach to PG composition analysis with i) a protocol that enables efficient PG isolation and purification without harsh chemical treatment to preserve PG modifications, and ii) a method for liquid chromatography/mass spectrometry (LC/MS) analysis using in silico muropeptide library for identification and quantification. Our PG data shows that bacterial PG composition is dynamic, remarkably able to modify their PG composition in response to the challenging external environment including growth conditions and antibiotic exposures in order to better adapt to survive. Our approach provides unprecedented molecular details into variations in PG modifications by pathogens and offers fundamental insight into bacterial physiology and mechanisms of microbial pathogenesis.