Mycobacterium leprae

1. Mycobacterium leprae
Presented by:
M. S. Deepak Kannan (BP211521)
I M.Sc. Applied microbiology
Department of microbiology
Sacred heart college (Autonomous)
Tirupattur
Presented to:
Dr. P. Saranraj
Head,
Department of microbiology
Sacred heart college (Autonomous)
Tirupattur

2. Content
 Introduction
 Morphology
 Pathogenesis of Mycobacterium leprae
 Tuberculoid
 Lepromatous
 Clinical Diseases by Mycobacterium leprae
 Laboratory Diagnosis
 Treatment
 Prevention
 Reference

3. Introduction
 Leprosy is a chronic granulomatous disease of man involving in skin as primary, peripheral
nerves and nasal mucosa but capable of affecting tissue or organs. It is one of the nervous
system infections.
 Leprosy is also called Hansen’s disease because Hansen first observed lepra bacilli in
1868.
 In 1970, Mycobacterium leprae causes a systemic infection in the nine-branded
armadillo.

4. Morphology
 Mycobacterium leprae is a rod-shaped bacterium which stains poorly by gram stain because its cell wall
contains lipids (mycolic acids). And also called as Hansen’s Bacillus spirally.
 Acid fast bacilli
 Intracellular parasite. Unable to be cultured on artificial media.
 Non – Motile, Non – capsulated, Non – sporing
 Microaerophilic respiration
 Optimum temperature is 27 ͦ - 30 ͦ C.
 Optimum pH is 7.
 It may found in air, water and soil.
 Mycobacterium leprae has a long generation time of about 12 days.

5. Pathogenesis of Mycobacterium leprae
 The transmission of disease by person to person infectious air borne nasal secretions or
droplets or aerosols are spread.
 The incubation period of Mycobacterium leprae multiplies slowly, it takes 5 years.
 Symptoms can take as long as 20 years to appear.
 The classification of leprosy are tuberculoid and lepromatous forms.

6. Tuberculoid
 The skin biopsy specimens show mature granuloma formation in the dermis that consist of
epitheloid cells, giant cells and marked infiltration of lymphocytes.
 Acid-fast bacilli usually cannot be demonstrated. The organisms invade the nerves and
selectively colonize the Schwann cells.
 The larger nerves are swollen and destroyed by granulomas.
 The nerve damage is non-specific and arises as a consequence of cell-mediated immune
response.

7. Lepromatous
 No cellular immune response.
 The lesions are small and many. They are shiny with no loss of feeling.
 Skin and nasal smears contain many bacteria. 10⁹ bacilli may observed per gram of
tissue.
 Organisms tend to invade vascular channels, the results in continuous bacteraemia
and consistent involvement of the reticuloendothelial system.
 The nerves are also infected but are less compared to tuberculoid type.

8. Clinical diseases by Mycobacterium leprae
 Leprosy is a chronic infection that affects the Skin and Peripheral nerves.
 The spectrum of tissue involvement is influenced by the patient’s immune status.
 The Tuberculoid form is milder and is characterized by Hypopigmented skin macules.
 The Lepromatous form is associated with
a) Disfiguring skin lesions
b) Nodules
c) Plaques Thickened dermis
d) Involvement of the nasal mucosa.

9. Laboratory diagnosis
 Specimen – skin biopsy, scraping from lesions and nasal mucosa.
 The microscopic examination by doing acid fast straining.
 Bacteriological index (BI) – BI is an expression of the extent of bacterial loads where as
Morphological index (MI) is calculated by counting the numbers of solid-staining acid-fast rods.
 The results are expressed as
A. 1+ - Atleast 1 Acid Fast Bacilli in every 100 fields,
B. 2+ - Atleast 1 Acid Fast Bacilli in every 10 fields,
C. 3+ - Atleast 1 Acid Fast Bacilli in every fields,
D. 4+ - Atleast 10 Acid Fast Bacilli in every fields,
E. 5+ - Atleast 100 Acid Fast Bacilli in every fields,
F. 6+ - Atleast 1000 Acid Fast Bacilli in every fields.

10. Laboratory diagnosis
 Mycobacterium leprae has not yet been successfully cultured in vitro but it can be grown in the laboratory by injection into the
foot pads of mice. It is a slow growing pathogen with the doubling time of 14 days.
 Lepromin skin test
 The Lepromin skin test is not used to diagnose leprosy but to determine what type of leprosy a person has. The lepromin
test is used to study host immunity to Mycobacterium leprae.
 Lepromin skin test is similar to Tuberculin test. An extract of Mycobacterium leprae is injected intradermally and
induration is observed 48 hours later in those whom a cell-mediated immune response against organism exist.
 Lepromin skin test is in two types of reaction, they are Fernandez reaction and Mitsuda reaction.
 Immunodiagnostic - Latex Agglutination Test, ELISA, FLA-ABS (Fluorescent leprosy antibody absorption test)
 Molecular analysis - Polymerase Chain Reaction (PCR) can be used as a means of diagnosis of leprosy and also as a tool for
drug assessment.

11. Treatment and Prevention
 Tuberculoid form is treated with Rifampicin and Dapsone for 6 months.
 Clofazimine is added to this regimen for treatment of the Lepromatous form, and therapy is extended to a
minimum of 12 months.
 The preventive and control measures includes
A. Early diagnosis and treatment
B. Vaccines (BCG Vaccine)
C. Chemoprophylaxis
D. Health education

12. Reference
 A textbook of microbiology by Ananthanarayan and Panikar (9th Edition) Pg. No: 364 –
369.
 Medical Microbiology by S. Rajan Pg. No: 189 – 193.
 Medical Bacteriology (Chapter-32) by Dr. P. Saranraj Pg. No: 157 – 162.

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