Investigation of mycobacterial colonisation and invasion of the respiratory mucosa

Background: The pathogenesis of Mycobacterium avium complex and Mycobacterium tuberculosis in the respiratory tract is poorly understood, as are the reasons for their differing virulence. We have previously shown that their initial adherence to the mucoso is identical. Methods: The interaction of M avium complex, M tuberculosis, and M smegmatis with human respiratory tissue was investigated in an organ culture model with an air interface. Tissue was infected for intervals up to 14 days and assessed by scanning electron microscopy for adherent bacteria or cultured for recoverable bacteria. Results: The mean number of adherent bacteria/mm(2) (and the viable count of macerated tissue, cfu/ml) at 15 minutes, 3 and 24 hours, 7 and 14 days were: M avium complex 168 (153), 209 (136), 289 (344), 193 (313), 14140 (16544); M tuberculosis 30 (37), 39 (23), 48 (53), 1 (760), 76 (2186); M smegmatis 108 (176), 49 (133), 97 (81), 114 (427), 34 (58), (n=6). There was no significant change in morphology between infected and uninfected tissue or tissue infected with the different species over 14 days. The number of M avium complex on the mucosa and recovered from tissue increased over time (p=0.03). M tuberculosis decreased on the surface, but recoverable bacteria increased (p=0.01). M smegmatis numbers on the mucosa and recovered from tissue decreased. Sectioned tissue showed M avium complex and M tuberculosis in submucosal mucus glands and M tuberculosis penetrating epithelial cells in one experiment. Conclusions: The initial adherence to the mucoso of the three species was similar, but after 14 days they varied in their interaction with the tissue in a manner compatible with their pathogenicity.