Analysis of the lipid composition of mycobacteria by thin layer chromatography

Mycobacteria species can differ from one another in the rate of growth, presence of pigmentation, the colony morphology displayed on solid media, as well as other phenotypic characteristics. However, they all have in common the most relevant character of mycobacteria: its unique and highly hydrophobic cell wall. Mycobacteria species contain a membrane-covalent linked complex that includes arabinogalactan, peptidoglycan, and long-chains of mycolic acids with types that differ between mycobacteria species. Additionally, mycobacteria can also produce lipids that are located, non-covalently linked, on their cell surfaces, such as phthiocerol dimycocerosates (PDIM), phenolic glycolipids (PGL), glycopeptidolipids (GPL), acyltrehaloses (AT), or phosphatidil-inositol mannosides (PIM), among others. Some of them are considered virulence factors in pathogenic mycobacteria, or critical antigenic lipids in host-mycobacteria interaction. For these reasons, there is a significant interest in the study of mycobacterial lipids due to their application in several fields, from understanding their role in the pathogenicity of mycobacteria infections, to a possible implication as immunomodulatory agents for the treatment of infectious diseases and other pathologies such as cancer. Here, a simple approach to extract and analyze the total lipid content and the mycolic acid composition of mycobacteria cells grown in a solid medium using mixtures of organic solvents is presented. Once the lipid extracts are obtained, thin-layer chromatography (TLC) is performed to monitor the extracted compounds. The example experiment is performed with four different mycobacteria: the environmental fast-growing Mycolicibacterium brumae and Mycolicibacterium fortuitum, the attenuated slow-growing Mycobacterium bovis bacillus Calmette-Guérin (BCG), and the opportunistic pathogen fast-growing Mycobacterium abscessus, demonstrating that methods shown in the present protocol can be used to a wide range of mycobacteria.