Intact pks 15 / 1 in Non – W-Beijing Mycobacterium tuberculosis Isolates

T structurally related families of cell envelope lipids, phthiocerol diesters and phenolic glycolipids, are virulence factors of Mycobacterium tuberculosis and M. leprae. They are also produced by other slow-growing species, in particular the pathogenic species M. marinum, M. ulcerans, and members of M. tuberculosis complex (1). Phthiocerol diesters are composed of a mixture of long chain β-diols that are esterified by multimethyl-branched fatty acids. Depending on the asymmetric centers bearing the methyl branches (D or L series), the fatty acids are called mycocerosic or phthioceranic acids, respectively, and the corresponding complex lipids are named dimycocerosates of phthiocerol (DIMs) or diphthioceranates of phthiocerol (DIPs) (1). The phenolic glycolipids (PGLs) consist of a lipid core similar to those of DIMs or DIPs but ω-terminated by an aromatic nucleus that is glycosylated by typeor species-specific mono-, tri-, or tetrasaccharide. Several lines of evidences suggest that PGLs are involved in the pathogenesis of mycobacterial infections. PGL-1 from M. leprae inhibits the proliferation of T lymphocytes after stimulation with concanavalin A (2). Moreover, PGL1 seems to be associated with resistance to intracellular killing by macrophages (3) and promotes phagocytosis of M. leprae by macrophages and Schwann cells by binding to complement component C3 or laminin α2 chain, respectively (4,5). Similarly, PGLs produced by a subset of M. tuberculosis isolates inhibit the host Th1-type T-cell and cytokine response (6). All M. tuberculosis strains tested that produce PGLs belong to the W-Beijing family and show a “hypervirulent” phenotype, in comparison with the clinical isolate M. tuberculosis CDC1551 and the laboratory strain M. tuberculosis H37Rv in the murine model (6) and rabbit model of meningitis (7). Previous study identified the involvement of the gene pks15/1 in the biosynthesis of PGLs; disruption of this gene generated a PGL-deficient mutant (8). Sequence alignment of the pks15/1 gene, when compared to the non–PGL-producing strains, M. tuberculosis H37Rv, Erdman, Mt103, and CDC1551, that contain 2 open reading frames [pks1 (Rv2946c) and pks15 (Rv2947c)], showed a 7-bp insertion in PGL-producing strains M. tuberculosis strain 210, belonging to the W-Beijing family, and M. canetti, whereas M. bovis and M. bovis BCG contained only a guanine insertion. This 7-bp or 1-bp insertion causes a frameshift mutation in the pks15, resulting in an intact pks15/1 with additional codons (8). Similar results have been shown in other W-Beijing strains, M. tuberculosis HN878, W4, and W10, which contain the 7-bp insertion and produce PGLs (6). In Thailand, the Beijing genotype is the predominant genotype among tuberculosis (TB) patients, particularly in patients with TB meningitis (unpub. data), which suggests recent transmission of this genotype in the country. Similarly, the Beijing genotype has been found frequently in Asia (9–11). Previous studies have shown that the M. tuberculosis strains belonging to this genotype contain an intact pks15/1 and can produce PGLs that associated with the hypervirulent phenotype (6,7). The goal of our study was to determine whether the hypervirulence of the WBeijing strains due to the ability to produce PGLs is unique among this family by investigating the pks15/1 gene of the Beijing strains compared to other strains that can cause diseases similar to those caused by Beijing strains.