Mycobacterium tuberculosis (Mtb) has been the leading cause of infectious disease mortality worldwide for the
past few decades with more than 1 million deaths annually. This pathogen has an exceptionally complex cell
wall structure, the outer components of which are important for direct interactions with the host, for giving
structural support and maintaining a hydrophobic barrier for small molecules and antibiotics. Phthiocerol
dimycocerosate (PDIM) is a lipid found in the outer-most layer of the Mtb cell envelope. PDIMs form a
permeability barrier, protecting the bacteria from antimicrobial compounds, and are important virulence factors
for defense against the host immune system.
Paradoxically, despite these important functions, PDIM is dispensable in vitro and its loss confers a growth
advantage leading to the selection of spontaneously occurring PDIM negative clones in laboratory cultures. This
affects experimental reliability, reproducibly and the interpretation of results. PDIM loss leads to reduced cell wall
permeability and virulence attenuation, producing misleading results in infection experiments, drug susceptibility
testing and genetic manipulations. To remove PDIM bias from TB research, and to study PDIMs role in
pathogenesis and drug tolerance, we need appropriate screening and selection tools.
In this grant application we will build on powerful new preliminary results to develop robust PDIM
selection, screening and cleanup protocols, determine the propensity of PDIM loss in different Mtb strains and
its impact on virulence, and aim to study how PDIM population heterogeneity and propionate metabolism impact
infectivity and antibiotic persistence.