Transepithelial migration of Mycobacterium tuberculosis strains and their affinity for glial cells in vitro.
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Background: Tuberculosis is an infectious disease caused by the bacillus M. tuberculosis. It is a disease that mainly infects the lungs, however, almost any other organ of the body can be infected. Central nervous system TB is a severe form of extrapulmonary TB representing 5 – 15 % of all cases of extrapulmonary TB and accounts for approximately 1 % of all TB cases. Microglia, the resident macrophages of the CNS, are located within the cerebral parenchyma by the BBB. These cells play a role as the first barrier against intra-cerebral infections such as TB. It is unknown whether the susceptibility characteristics of M. tuberculosis strains affects the rate at which the bacteria migrate through the alveolar epithelium to other sites of the body. Materials and methods: M059K glial cells were cultured in a 24-well tissue culture plate then infected with different strains of M. tuberculosis (susceptible F1, MDR F28, susceptible and XDR Beijing, and susceptible, MDR and XDR F15/LAM4/KZN) at an MOI of 10. A549 alveolar epithelial cells and M059k glial cells were co-cultured in a 24-well transwell plate. A549 cells were cultured on the insert membranes and M059K glial cells in the wells below the inserts. The A549 cell monolayers were exposed to the different strains. The H37Rv laboratory strain was included as a reference strain. Results: Invasion capacity, transmigration rate, adhesion and invasion rate following transmigration were established. The susceptible F15/LAM4/KZN and F11 strains showed a high invasion capacity for glial cells while the susceptible Beijing strain showed the lowest invasion capacity. The XDR strains displayed a greater transmigration rate over time. The MDR strains demonstrated lower transmigration rates compared to the susceptible strains. Only the susceptible Beijing strain did not show any transmigration ability. Following transmigration, the XDR strains demonstrated significantly high adhesion and invasion rates. The susceptible Beijing strain still did not show any dissemination ability. Discussion: We found differences in invasion capacity and transmigration ability between the different strains of M. tuberculosis. The invasion capacity of M. tuberculosis into glial cells could differ from that of M. tuberculosis directly inoculated onto the glial cells. This could be a result of structural changes on the bacterial surface while migrating through the epithelium. Conclusion: We conclude that M. tuberculosis isolates are able to pass through the epithelial lining of the alveoli to other body sites by transepithelial migration, and the XDR isolates pass A549 cells very effectively.