<prompt> Not true about tubercular bacilli -Facultative anaerobeDiscovered by Robert KochGram positiveHas thick cell wall  <response>: Ans. is a i.e., Facultative anaerobe M. tuberculosis was discovered by Robert koch. M. tuberculosis is gram-positive, obligate aerobe, acid-fast, straight or slightly curved rod. Electron microscopy shows thick cell wall. M. tuberculosis is acid-fast bacillus and resists decolorization by 20 H2SO4. Acid fastness depends on presence of high content ofmycolic acid in cell membrane most important factor and also on integrity of cell wall. M. tuberculosis is also alcohol fast as it resists decolorization by absolute alcohol. Fluorescence microscopy using auramine rhodamine stain is used when several smear are to be examined daily. It is much less tiring to microscopist and is more sensitive than acid fast staining. 