EXTRACELLULAR ENZYME-ACTIVITIES POTENTIALLY INVOLVED IN THE PATHOGENICITY OF MYCOBACTERIUM-TUBERCULOSIS

To evaluate the potential contribution of extracellular enzymes to the pathogenicity of mycobacteria, the presence of selected enzyme activi ties was investigated in the culture filtrates of the obligate human p athogen Mycobacterium tuberculosis, M. bovis BCG, the opportunistic pa thogens M. kansasii and M. fortuitum, and the non-pathogenic species M . phlei and M. smegmatis. For M. tuberculosis and M. bovis, 22 enzyme activities were detected in the culture filtrates and/or cell surfaces , of which eight were absent from the culture fluids of non-pathogens: alanine dehydrogenase, glutamine synthetase, nicotinamidase, isonicot inamidase, superoxide dismutase, catalase, peroxidase and alcohol dehy drogenase. These activities, which correspond to secreted enzymes, for med a significant part (up to 92%) of the total enzyme activities of t he bacteria and were absent from the culture fluids and the cell surfa ces of the non-pathogenic species M. smegmatis and M. phlei. The extra cellular location of superoxide dismutase and glutamine synthetase see med to be restricted to the obligate pathogens examined. The differenc e in the enzyme profiles was not attributable to the growth rates of t he two groups of bacteria. The presence of the eight enzyme activities in the outermost compartments of obligate pathogens and their absence in those of non-pathogens provides further evidence that these enzyme s may be involved in the pathogenicity of mycobacteria. In addition, t he eight enzyme activities were demonstrated in the cell extract of M. smegmatis. Stepwise erosion of the cell surface of M. smegmatis to ex pose internal capsular constituents showed that the various enzyme act ivities, with the possible exception of superoxide dismutase, were loc ated more deeply in the cell envelope of this bacterium. This suggests that the molecular architecture of the mycobacterial envelopes may pl ay an important role in the pathogenicity of these organisms.