10 - Detection and Characterization of Mycolic Acids and Their Use in Taxonomy and Classification

Abstract

Abstract Mycolic acids are high molecular weight α-alkyl-branched β-hydroxy fatty acids found in the cell wall lipids of acid-fast bacteria. Mycobacterial mycolic acids are among the longest chain (contain between 60 and 90 carbon atoms) and usually occur as complex mixtures of structurally related molecules having oxygen functions such as carboxy, epoxy, keto or methoxy groups in addition to the 3-hydroxy unit and combinations of cis or trans double bonds or cyclopropane rings, methyl branches also being encountered. Mycolic acid from other members of the suborder Corynebacterineae contains between 22 and 78 carbon atoms and desaturation is the only form of functionalization found in them. A wide array of chemical methods is used for mycolic acid analysis. Thin-layer chromatography (TLC) provides a simple method for distinguishing mycobacteria from related genera that produces mycolic acids. Both one- and two-dimensional TLC methodology, employing a variety of solvents, has been used. Molecular heterogeneity of individual mycolic acid classes can be assessed without pyrolysis by gas–liquid chromatography (GLC) or combined gas chromatography–mass spectrometry (GC–MS) of trimethylsilyl ether derivatives of mycolates. Profiling of mycolic acid is a potential tool in distinguishing between acid-fast bacteria including Mycobacterium and related genera of the suborder Corynebacterineae . The GLC pattern is regarded as a fingerprint characteristic for certain species. High-performance liquid chromatography enables separation of p -bromophenacyl esters of mycolate into classes, and homologous components are resolved by reverse-phase chromatography. The generated mycolate profiles are characteristic for many mycobacterial species and these have been used diagnostically.