Protein expression in Mycobacterium tuberculosis differs with growth stage and strain type

Different phenotypes are displayed by Mycobacterium tuberculosis (M. tuberculosis) strains, fuelling speculation that certain strains are "hypervirulent" and able to evade host defenses better than others. Furthermore, differential antigen expression by M. tuberculosis strains may explain why certain patients are susceptible to a repeat episode of tuberculosis. The objective of this study was to compare protein expression by M. tuberculosis H37Rv and clinical isolates in order to determine whether differential protein expression contributes to the different phenotypes expressed by these strains. Expression of alpha-crystallin, the antigen 85 complex, PstS-1, L-alanine dehydrogenase and the 65 kDa antigen was analysed by Western blotting and enzyme-linked immunosorbent assays, using mouse monoclonal antibodies. We found no significant difference in the growth rate of the M. tuberculosis strains in vitro, and although M. tuberculosis protein expression showed phase variation during growth, expression seemed to be qualitatively, but not quantitatively, conserved in the strains investigated. These results have potentially important implications for vaccine development and serodiagnosis.