STRUCTURES OF THE GLYCOLIPID ANTIGENS OF MEMBERS OF THE 3RD BIOVARIANT COMPLEX OF MYCOBACTERIUM-FORTUITUM

Among the fast-growing mycobacteria, members of the Mycobacterium fort uitum complex are the most-commonly cited opportunistic human pathogen s, notably in post-surgical infections. Previous studies showed that t his complex was composed of four well-identified species and a group o f isolates that did not correspond to recognized species, which has be en referred to as the third biovariant complex. The occurrence and che mical structure of the glycolipid antigens of six strains that belong to this latter group were examined in the present study. Based on the TLC profiles, resistance to alkali and seroreactivities of their glyco lipids, the examined strains were classified into three groups: one gr oup was devoid of species-specific glycolipid and the two other groups contained alkali-stable or alkali-labile glycoconjugates. The structu res of the major glycolipid antigens of the latter two groups were elu cidated by fast-atom-bombardment MS, one-dimensional and two-dimension al NMR spectroscopy and conventional chemical analyses. The alkali-sta ble glycolipids were structurally identical to the C-myoside-type glyc opeptidolipids characterized in the taxonomically related species Myco bacterium peregrinum. The major alkali-labile glycolipid was identifie d as 6)-alpha-Glcp2Acyl-(1-->1)-alpha-Glcp3,4,6Acyl(3). The acyl subst ituents consisted of one acetyl group and three fatty acyl residues co mposed mainly of tetradecanoyl residues, but significant amounts of 2- methylhexadecanoyl and 2-methyloctadecanoyl substituents were also pre sent. The heterogeneity of the glycolipid content of members of the th ird biovariant complex of M. fortuitum demonstrated in the present stu dy confirms the heterogeneity of the complex. In addition, the occurre nce of a species-specific glycolipid in some strains supports the hypo thesis that some strains of this complex of M. fortuitum may belong to a new mycobacterial species.