Overview Of History

Mycobacterium tuberculosis was first isolated on 24th March 1882 by a German Physician Robert Koch, who received a Nobel Prize for this discovery in 1905 (1). Tuberculosis is one of the oldest diseases in the history of mankind with evidence of tubercular decay found in some Egyptian mummies from 3000-2400 BC (2). The study of tuberculosis was also known as phthisiatry from phthisis, the Greek term for tuberculosis. Hippocrates identified phthisis as the most widespread disease of the time which involved the coughing up of blood, fever and was almost always fatal (3). Avicenna first identified that pulmonary TB was an infectious disease and developed the method of quarantine in order to limit the spread of disease (4 & 5). The disease was given the name of tuberculosis in 1839 by JL Schonlein (6).

Burden Of Disease

Tuberculosis (TB) is an infectious disease caused by various strains of mycobacteria; of which the commonest cause is Mycobacterium tuberculosis (7). The disease can affect any part of human body but commonly attacks the lungs. One third of the world's current population has been infected by Mycobacterium tuberculosis and new infections occur at a rate of 1 per second (8). About 5-10% of these infections leads to active disease which, if left untreated, kills about 50% of its victims. TB affects approximately 8 million people worldwide and about 2 million people die of this disease annually. In the 19th century pandemic tuberculosis killed about 1/4th of the adult population of Europe (9). Nevertheless, these figures may be only the tip of the iceberg. Tuberculosis is again on the rise and main cause for the resurgence of TB is immunodeficiency as a result of HIV co-infection or, less commonly, immunosuppressive treatment such as chemotherapy or corticosteroids.

Introduction To Mycobacteria

Mycobacteria are aerobic and non-motile bacteria (with the exception of Mycobacterium marinum which is motile within macrophages) which are characteristically alcohol-acid fast (10). They are present in the environment widely in water and various food sources. They are usually considered to be Gram-positive bacteria, but they do not generally retain the crystal violet stain and are thus called Gram-positive acid-fast bacteria. These acid-fast bacilli (AFB) are straight or slightly curved rods 0.2-0.6 mm wide and 1-10 mm long. Mycobacteria are classified on the basis of growth & their ability to produce pigment.

On the basis of growth:

* Rapid growing: Mycobacteria that forms colonies clearly visible to naked eye within 7 days on sub-cultures

* Slowly growing: Mycobacteria that do not form colonies clearly visible to naked eye within 7 days on sub-culture

On the basis of pigmentation mycobacteria are divided into 3 groups:

* Photochromogens (Group I): Produce non-pigmented colonies in dark and pigmented colonies when exposed to light and re-incubation e.g., M. kansasii, M. marinum etc

* Scotochromogens (Group II): Produce deep yellow to orange colonies when grown in the presence of either light or darkness e.g., M. scrofulaceum, M. xenopi etc

* Non-chromogens (Group III & IV): Non-pigmented in light and dark or only...