Virulence of selected Mycobacterium tuberculosis clinical isolates in the rabbit model of meningitis is dependent on phenolic glycolipid produced by the bacilli

Infection with Mycobacterium tuberculosis in humans results in active disease in similar to 10% of immune-competent individuals, with the most-severe clinical manifestations observed when the bacilli infect the central nervous system (CNS). Here, we use a rabbit model of tuberculous meningitis to evaluate the severity of disease caused by the M. tuberculosis clinical isolates CDC1551, a highly immunogenic strain, and HN878 or W4, 2 members of the W/Beijing family of strains. Compared with infection with CDC1551, CNS infection with HN878 or W4 resulted in higher bacillary loads in the cerebrospinal fluid and brain, increased dissemination of bacilli to other organs, persistent levels of tumor necrosis factor-a, higher leukocytosis, and more-severe clinical manifestations. This pathogenic process is associated with the production by HN878 of a polyketide synthase derived phenolic glycolipid (PGL), as demonstrated by reduced virulence in rabbits infected with an HN878 mutant disrupted in the pks1-15 gene, which is required for PGL synthesis.