Extrapulmonary Locations of Mycobacterium tuberculosis DNA During Latent Infection

Background. One-third of the world's population has latent infection with Mycobacterium tuberculosis, and 10%-15% of cases of reactivation occur at extrapulmonary sites without active pulmonary tuberculosis. Methods. To establish the frequency and location of mycobacterial DNA, organ specimens from 49 individuals who died from causes other than tuberculosis were studied by means of polymerase chain reaction (PCR), PCR plus DNA hybridization, in situ PCR, real-time PCR, and spoligotyping. Results. Lung specimens from most subjects (36) were positive for M. tuberculosis, as were specimens from the spleen (from 35 subjects), kidney (from 34), and liver (from 33). By in situ PCR, mycobacterial DNA was found in endothelium, pneumocytes, and macrophages from the lung and in Bowman's parietal cells and convoluted proximal tubules from the kidney. In spleen, macrophages and sinusoidal endothelial cells were positive, whereas in liver, Kupffer cells and sinusoidal endothelium were commonly positive. Spoligotyping of 54 pulmonary and extrapulmonary positive tissues from 30 subjects showed 43 different genotypes, including 36 orphan types. To confirm the viability of mycobacteria, 10 positive tissue samples were selected for isolation of mycobacterial RNA. All samples showed 16S ribosomal RNA expression, while 8 and 4 samples showed expression of the latent infection genes encoding isocitrate lyase and alpha-crystallin, respectively. Conclusions. M. tuberculosis persists in several sites and cell types that might constitute reservoirs that can reactivate infection, producing extrapulmonary tuberculosis without lung involvement.