For many years, citizens of well-developed countries believed tuberculosis (TB) was an illness of the past. Tuberculosis is an infectious disease that can be caused by various strains of mycobacterium, primarily Mycobacterium tuberculosis (MTB). Mycobacterium tuberculosis has a waxy coating on its cell surface that makes it highly resistant to Gram staining, and consequently must be identified using Acid-fast techniques. Despite its resistance to Gram staining, Mycobacterium tuberculosis is classified as an acid-fast Gram-positive bacteria due to its lack of an outer cell membrane. Along with its resistance to stains, the cell wall has many characteristics that currently make it the center of many new studies. As some researchers struggle to understand the exact reasons for the re-emergence of tuberculosis, others are seeking new mechanisms and ways to inhibit the disease. (1)
Mycobacterium tuberculosis, first discovered by Robert Koch in 1882 is an aerobic bacillus. Mycobacterium tuberculosis is naturally a pathogen of the mammalian respiratory system due to its need for an oxygen rich environment. Cell division occurs at an unusually slow pace in this species. Cell division can take anywhere from 15 to 20 hours, which is extremely sluggish in comparison to other bacteria. This bacterium requires very little water activity and can survive in a dry state for long periods of time. The lipid rich cell wall of Mycobacterium tuberculosis is responsible for the organism’s ability to withstand disinfectants and ability to act in a virulent manner.
Alveolar macrophages in the lungs take up Mycobacterium tuberculosis, but are incapable of digesting the bacterium. The cell wall of the bacterium inhibits fusion of the phagosome with a lysosome by blocking a bridging molecule known as early endosomal autoantigen 1 (EEA1). The obstruction of the bridging molecule however does not affect the ability of nutrient filled vesicles to fuse with the bacterium. This characteristic allows the bacterium to grow and multiply unchecked within a macrophage. Mycobacterium tuberculosis carries a gene that hinders the acidification of a phagosome. Micro-evolutionary variation has influenced the fitness and transmission dynamics of Mycobacterium tuberculosis strains. (2)
In 1998 the genome of the H37Rv strain of Mycobacterium tuberculosis was published. The genome consists of four million base pairs and 3,959 genes. The genome includes 250 genes that are used in the metabolism of fatty acids. Thirty-nine of the 250 genes used for the metabolism of fatty acids are responsible for the polyketide metabolism that generates the waxy coat, this suggests that the waxy coat serves an important role in pathogen survival.
Researchers have three theories as to why tuberculosis has begun to reemerge in developed countries. The first theory involves the ability of Mycobacterium tuberculosis to change between a dormant state and a replicative state. The bacterium can transition from...