<prompt> Which of the following are acid fast positive with 20 sulphuric acid:M. aviumM. lepraeM. tuberculosisNocardia  <response>: Ans. c M. tuberculosis Features M. tuberculosis M. leprae Acid fastness Resist decolorization by 20 H2SO4 Resist decolorization by 5 H2SO4 Alcohol fastness Present Absent Culture Possible Not possible Niacin Positive also some strain of M. microti Negative Generation time 14-15 hours 12-1 3 days Remember:- Nocardia resist 1-4 of sulphuric acid weakly acid fast. 