Mycobacterium leprae - Classification, Morphology, Culture, Cell wall, Antigen, Characteristics

Classification of Mycobacterium leprae

Mycobacterium leprae can be classified phenotypically by:

Domain: Bacteria

Phylum: Actinomycetota

Class: Actinomycetia

Order: Mycobacteriales

Family: Mycobacteriaceae

Genus: Mycobacterium

Species: lepra

Characteristics of

Mycobacterium leprae causes leprosy, a chronic infectious disease that affects the skin, peripheral nerves, and mucosa of the upper respiratory and the eyes. It is the only mycobacterium known to cause infection of the nervous system. It is mainly transmitted via the respiratory tract or skin and has a long incubation period (2-5 years).

Morphology

Mycobacterium leprae is less acid-fast than Mycobacterium tuberculosis. Hence, 5% sulphuric acid, instead of 20% is used for decolorization. The bacterium is non-motile, non-sporing, gram-positive, and stains more readily than Mycobacterium tuberculosis.

Morphologically, Mycobacterium leprae also exhibits cubical, lateral, and even branching forms measuring 1-8 x 0.2-0.5 μm. It is a slightly curved or straight rod with parallel sides and surrounded ends. It is an obligate intracellular bacterium that multiplies in tissues at a cooler temperature.

Cultural characteristics of Mycobacterium leprae

Mycobacterium leprae has not been cultured in-vitro like bacteriological media and tissue culture

Footpads of mice

• footpads of mice are used as a standard procedure for experimental works of Mycobacterium leprae

• intradermal inoculation of lepra bacilli into the footpads of mice results in the development of granuloma at the site of inoculation in 1-6 months

Nine-banded armadillo

• the nine-banded armadillo is highly susceptible to Mycobacterium leprae

• Mycobacterium leprae in these animals produces a lesion typical of lepromatous leprosy

• This animal is now used for genetic studies including the development of vaccines

Cell wall components of Mycobacterium leprae

The cell wall components of Mycobacterium leprae stimulate the production of antibodies and the cell-mediated response. The cell wall of Mycobacterium leprae consists of four layers:

• Peptidoglycan is the innermost layer, which gives the bacteria rigidity and shape

• Liparabinomannose-B (LAM-B) is the latter next to the peptidoglycan layer

• Mycolic acid is the third layer attached to the LAM-B membrane

• Mycosides are the outermost fourth layer of the cell wall. Phenolic glycolipid (PGL-1) is the major component of the outermost layer of the cell wall.

Antigenic structure of Mycobacterium leprae

Mycobacterium leprae contains a wide variety of mycobacterial Ag. LAM-B is a major Ag of Mycobacterium leprae and is highly immunogenic and induces a high level of serum antibodies. PGL-1 is also the major antigen component of the outermost layer of the cell wall.