EFFECTS OF ISONIAZID ON ULTRASTRUCTURE OF MYCOBACTERIUM-AURUM AND MYCOBACTERIUM-TUBERCULOSIS AND ON PRODUCTION OF SECRETED PROTEINS

Isoniazid (INH), one of the most effective antimycobacterial drugs, sp ecifically inhibits, at an early stage of its action, the biosynthesis of mycolic acids, specific mycobacterial lipids which play a central role in the cell envelope architecture of mycobacteria. In the present study, the consequences of the action of INH on the cell morphology o f Mycobacterium tuberculosis and Mycobacterium aurum were examined, El ectron microscopy was used to observe bacilli which were previously tr eated with either subinhibitory concentrations of INH or the MIC of th e drug, leading to a decrease of 20 to 35% (by weight) of their mycoli c acid contents, The earlier effect of INH on the ultrastructure of my cobacteria, as revealed by negative staining of bacilli, was the alter ation of the bacterial poles; this event was observed prior to the bac teriostatic action of the drug and was accompanied by a release of mat erial from the poles into the extracellular medium, In a later stage o f the drug's action, cell deformation occurred and more extracellular material was seen, The material released following the action of the d rug on susceptible mycobacterial cells was identified as being almost exclusively composed of proteins, Labeling of amino acids with S-35 pr ior to and during the action of INH on M. aurum and subsequent analysi s of the labeled proteins led to the conclusion that they consisted of secreted proteins which were up to 20-fold oversecreted in the presen ce of the drug, Competitive enzyme-linked immunosorbent assay with the secreted 45/47-kDa antigen complex of M. tuberculosis demonstrated up to 20-fold oversecretion of these proteins, Taken together, the produ ction of oversecreted proteins following the decrease of the cell enve lope mycolate content by INH strongly suggests that mycolic acids may act as a barrier in the export of proteins secreted by mycobacteria.