Tubercle Bacilli in Spinal Tuberculosis - Morphology, Cell Wall Features, Behaviour and Drugs

Tubercle bacilli are tiny thin rod-shaped, non-spore-forming, non-motile obligate aerobic bacteria measuring 3 μm in length and 0.5 μm in width without pili for adherence and without producing adhesion molecule, and are acid-fast bacilli (AFB) with thick waxy cell wall having poorly developed porins, being present in the planktonic form. Tubercle bacilli are very slowly replicating (12 hours of generation time) only in presence of oxygen. Tuberculosis is a product of war between the host phagocytes and M tuberculosis in tissue. Phagocyte and M tuberculosis have very different cell wall composition, but both have very similar chemical weapons in them for fight and defense. Mycobacterium produces various mycolic acid compounds to form waxy cell wall and to defend it not to be digested by phagocytes, and not to be killed by the antituberculous drugs. Mycobacterium forms granuloma (tubercle) which is the specific reticuloendothelial tissue reaction to the specific type of irritants in normal person. It does not produce chondrolytic enzymes to destroy cartilage and disk, and does not adhere to any biomaterials. Thick waxy coat of Mycobacterium impedes the entry of nutrient through the poorly developed and scarce porins, and thus limits growth rate, but it also protects the bacilli from host defenses and antibiotics.