• Mycobacterium is a genus within the order of
• It compromises a large number of well characterized
• Several of which are associated with human and
animal diseases such as TB and leprosy.
• The genus Mycobacterium contains three groups.
Mycobacterium species …
• Obligate parasites: this includes
• 1. Mycobacterium Tuberculosis Complex(MTC):
• M. tuberculosis, M. bovis, M.africanum, M. canetti, M.microti,
M.caprae, M. pinnipeddi
• 2. Mycobacterium leprae
• Opportunistic pathogens
• These are the nontuberculosis Mycobacterium (NTM)
• they are categorized as
Mycobacterium species …
• Scotochromogen, Non-chromogens AND Rapid Growers
This is the traditional Runyon classification
M. tuberculosis M. bovis M.africanum
2. Photochromogens M. kansassi , M. marinum
3. Scotochromogen M. scrofulaceum, M. gordonae, M. szulgai
4. Non-chromogens M. avium-intracellulare, M. xenopi, M. terrae
5. Rapid growers M. fortuitum, M. abscessus, M. chelonae, M. Smegmatis
• Mycobacteria are Slender Rods
• They sometimes show branching, filamentous forms resembling
with fungi mycelium.
• They are aerobic, non motile, non capsulated and non spore
• usually having slow growth
• They are acid fast bacilli (AFB)
• Cell wall- rich in lipids
• The bacterium that causes Tuberculosis.
• TB also caused by M.bovis
• M.tuberculosis was discovered in 1882 by Robert Koch
• In tissue
• Mtb is a thin, straight or slightly curved rod(0.4× 3 µm) where as
M.bovis is straight rod and short (0.3×3 µm).
• On artificial media:
• Filamentous forms are seen with variable morphology from one
species to the an other.
• They occur singly, in pairs or as a small clumps.
Mtb on LJ medium
• They are obligate aerobic, non motile, non capsulated and non spore
• They are alcohol and acid fast.
• Slow growing ( doubling time 18hrs)
• cell wall: rigid, rich in lipids, hydrophobic, resistant to many
disinfectants, detergents, stains, antibiotics and host immune
• Relatively resistance acid and alkali
• 5% phenol, 15% H2 SO4, 3% nitric acid, 4% NaOH
• Resistance to dehydration:
• can survive
• expectorated sputum for 20-30 hrs and
• in droplet nuclei for 8-10 days.
• which is important for transmission by aerosols.
• Destroyed by 80% ethanol for 2 minutes and 5
minutes iodine solution.
• Sensitive to formaldehyde, glutaraldehyde
• Killed at 60℃ 𝑓𝑜𝑟 10 − 15 𝑚𝑖𝑛𝑢𝑡𝑒𝑠
• Culture may be killed by direct sunlight for 2hrs.
The Runyon classification of nontuberculous mycobacteria based on the rate of growth, production of yellow pigment and whether this pigment was produced in the dark or only after exposure to light.
On these bases, the nontuberculous mycobacteria are divided into four groups:
1. Runyon I (Photochromogens): slow growing, and produce a yellow-orange pigment when exposed to light. M. kansasii, M. marinum
2. Runyon II (Scotochromogens): slow growing, and produce a yellow-orange pigment in light or in the dark. M. scrofulaceum, M. gordonae, M. szulgai
3. Runyon III (Nonchromogenic): slow growing, and do not produce pigment. M. avium-intracellulare, M. xenopi, M. terrae
4. Runyon IV (Rapid Growers Runyon): rapid growing (colonies in 5 days). They do not produce pigment. M. fortuitum, M. peregrinum, M. abscessus, M. chelonae