The role of trehalose dimycolate (cord factor) on morphology of virulent M. tuberculosis in vitro

SummarySettingM. tuberculosis (MTB) lose virulence during prolonged culture on artificial media. This loss of virulence is associated with a change in colony morphology. Several studies suggested that trehalose 6,6′ dimycolate (TDM or cord factor), contributes to colony morphology.ObjectiveTo investigate the role of TDM in colony morphology of MTB using clinical isolates selected to have colony morphology typical of virulent or attenuated organisms.DesignUse immunohistochemical and physical chemical methods to assess the presence and distribution of TDM in rapidly growing pellicles of MTB.ResultsTDM forms an insoluble crystalline monolayer at the air–water interfaces that is more rigid than that formed by any other biologic amphiphile and is strong enough to support a spreading pellicle of MTB. The surface of young pellicles of the isolate with virulent morphology displayed the regular linear pattern characteristic of monolayers of TDM. TDM was also identified in the open spaces of pellicles of MTB by immunohistochemistry. MTB with morphology of attenuated organisms had neither of these properties.ConclusionThese data suggest that the characteristic morphology of colonies of virulent MTB is due to TDM released from the surface of the organisms.