Properties and lab diagnosis of M. tuberculosis

1. MYCOBACTERIUM
TUBERCULOSIS
By Mrs Neha Rawat

2. INTRODUCTION
Family- Mycobacteriaceae
Order- Actinomycetales
Genus- Mycobaterium
Species- Mycobacterium tuberculosis
All the species under Mycobacterium
have two main properties Acid fastness
and Guanine plus cytosine content of
DNA of Mycobacterium is 61-71 mol%

3. Cont....
Mycobacterium are
1. Non motile
2. Non sporing
3. Non capsulated
4. Weakly gram positive
5. Straight or slightly curved rod shaped
6. Obligate aerobes
7. Shows fungus like branching resemling
fungal mycelium

4. History
Lepra bacillus discovered by Armeur
hansen (1864) known as Hansen’s bacilli
Robert Koch isolated the tubercle
bacillus in 1882

5. Mycobacterium tuberculosis complex
M.tuberculosis
M.bovis
M.caprae
M.africanum
M.microti
M.pinnipedii
M.canetti

6. Antigenic structure
 Antigens of M.tuberculosis are-
1. Cell wall consists of insoluble antigens such as
Peptidoglycan layer- maintains shape of cell,
Arabinogalacten layer- Facilitates survival of M.
Tuberculosis within the macrophages ,
Mycolic acid layer- responsible for acid fastness
and reduces the entry of most antibiotics ,
Outermost layer of lipids
Proteins
Plasma membrane

7. Cont....
2. Cytoplasmic soluble antigens- used in
serodiagnosis of tuberculosis

8. MORPHOLOGY
 M. tuberculosis organisms are straight or slightly
curved rods occurring singly, in pairs, or in small
clumps.
 They measure about 3×0.3 µm in size; sometimes
long filamentous forms are also seen. M. bovis is
usually shorter and stouter than M. tuberculosis.
 They are Gram positive but are difficult to stain.
They stain poorly with Gram staining.
 They are nonmotile, nonsporing, and
noncapsulated.