Biology Tuberculosis is caused by the bacterium Mycobacterium tuberculosis , also known as Bacillus tubercle . The morphology is thin rods, usually straight or slightly curved. It often appears singly and occasionally in threads. Bacillus tubercle is often difficult to stain because it is an acid-fast bacterium, which means it has the ability to retain the original stain even after washing it.
Mycobacterium tuberculosis has a thick, waxy coat that also makes the stain irregular.
Rather than using a Gram stain, a Zeihl-Nielson's stain is used. Zeihl-Nielson stain of sputum containing Mycobacterium tuberculosis Mycobacterium tuberculosis is an obligate aerobe that grows extremely slowly. In the lab, it may take up to 6 weeks for mycobacterium growth to appear on a medium, even when Lowenstein-Jensen's medium is used to enhance growth. The sluggish growth rate is a result of the tough cell wall that resists the passage of nutrients into the cell and inhibits waste products to be excreted out of the cell. The specialized cell envelope of Mycobacterium tuberculosis resembles a modified Gram positive cell wall.