Protection by live Mycobacterium habana vaccine against Mycobacterium tuberculosis H37Rv challenge in mice

In recent years the efficacy of BCG vaccine against tuberculosis has been questioned and there is no alternative vaccine available. Several strategies are being applied to get a satisfactory vaccine. Two approaches are generally considered: the subunit vaccines and the whole cell vaccines. The objective of this investigation was to evaluate an avirulent mycobacteria, Mycobacterium habana, as a whole cell vaccine to protect mice from infection of M. tuberculosis H37Rv.

AKR and immunocompromised SJL/J mice were immunized with live M. habana vaccine. These mice were challenged with M. tuberculosis H37Rv eight weeks later along with unimmunized control mice. Protection by M. habana vaccine was measured through several parameters, which included survival of challenged mice, dissemination of challenge strain and histopathology of lung tissues.

M. habana vaccinated animals were healthier than the unvaccinated mice after challenge with M. tuberculosis and survived with significant increase in mean survival time. The viable count of challenge strain was at least 100-fold less in vaccinated mice than the control mice. The lung tissues in unvaccinated mice showed marked bronchopneumonia with clusters of acid fast bacilli, whereas vaccinated mice showed small areas of damage and evidence of protection subsequently.

It may be concluded from the evidence presented here that mice vaccinated with M. habana were protected from challenge with M. tuberculosis in both normal and immunocompromised states.