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).