Method for Inactivating and Fixing Unstained Smear Preparations of Mycobacterium tuberculosis for Improved Laboratory Safety

The inactivation of smears that contain Mycobacterium tuberculosis for microscopy before removal of the material from a biosafety cabinet is an important safety factor in preventing the potential transmission of tuberculosis to laboratory workers. The fixing and inactivating properties of heat flaming, 70% ethanol, and 1, 3, and 5% phenol in ethanol for smears containing M. tuberculosis were investigated. Heat flaming failed to inactivate the smear material, whereas 5% phenol in ethanol successfully fixed and inactivated all smears containing M. tuberculosis both from concentrated sputum samples and from culture material.