Mycobacterium tuberculosis: General Properties

General Properties

Members belonging to the genus Mycobacterium show the following characteristics:

·           They are acid fast.

·           They contain mycolic acid, which consists of 60–90 carbons that are splitted to produce fatty acid methyl esters.

·           They contain a high (61–71%) guanine and cytosine content in the DNA.

The cell wall of Mycobacterium: The cell wall ofMycoba-cterium is complex. It is typical as that of Gram-positive bacteria. It contains unique cytoplasmic membrane, surrounded by a thick peptidoglycan and a layer of highly antigenic mycolic acid. It is thick and lipid rich. The complex cell wall confers many properties to the bacteria. The mycolic acid consists of peptidoglycolipids, glycolipids, and lipids. These account for nearly 60% of dry weight of the cell wall. The outer layer con-sists of peptic chains and is an important antigen of the bac-teria, which induces cellular immunity in infected patients. A purified protein derivative (PPD) of this layer is used as a source of antigen in the skin test to demonstrate hypersensi-tive reaction of the host to M. tuberculosis.