Few acid-fast organisms were detected, which is common in cases of simian tuberculosis. This animal had at least 5 negative tuberculin tests. Cynomolgus monkeys often respond poorly to tuberculin challenge, and may carry lesions of tuberculosis without evidence of clinical disease. In this monkey, abdominal lesions were more numerous and larger than pulmonary lesions. Organisms in the M. avium-intracellulare group are frequently isolated in macaques with mycobacterial infections in which tubercle formation is not a feature.
Mycobacterium tuberculosis has no known endotoxin or exotoxins.
Due to the presence of several compounds in their cell wall, mycobacteria are able to escape killing by phagocytic cells and induce delayed hypersensitivity. Cord factor is a surface glycolipid in the cell wall of M. tuberculosis . Absent from nonpathogenic mycobacteria, cord factor is known to stimulate granuloma formation. Sulfatides are sulfur containing glycolipids in the cell wall of mycobacteria that prevent fusion of phagosomes of macrophages containing M. tuberculosis with lysosomes. Another cell wall constituent, LAM, is a heteropolysaccharide similar to the endotoxins of gram-negative bacteria.