This document discusses Mycobacterium tuberculosis, the bacteria that causes tuberculosis. It begins by describing the genus Mycobacterium and some of the important species that cause diseases like tuberculosis and leprosy in humans. It then classifies mycobacteria into three groups: obligate parasites like M. tuberculosis and M. leprae, opportunistic pathogens, and saprophytes. The document goes on to describe the pathogenesis and transmission of M. tuberculosis, the immune response it elicits, and various laboratory methods for diagnosing tuberculosis like microscopy, culture, and antibody detection.

1. Ashish Kelwa
B.tech Bioinformatics
III Sem

2. INTRODUCTION
Mycobacterium, genus of rod-shaped bacteria of the
family Mycobacteriaceae (order Actinomycetales), the
most important species of which, M. tuberculosis and
M. leprae, cause tuberculosis and leprosy, respectively,
in humans. M. bovis causes tuberculosis in cattle and in
humans. Some mycobacteria are saprophytes (i.e., they
live on decaying organic matter), and others are
obligate parasites. Most are found in soil and water in a
free-living form or in diseased tissue of animals.
Streptomycin, rifampin, and species-specific
antimicrobial agents have had some success in treating
Mycobacterium infections. Mycobacterium leprae

3. Classification
 Mycobacteria are slender rods that sometimes show branching, filamentous
forms resembling fungal mycelium.
 The genus Mycobacterium contains three groups:
o Obligate parasites
o Opportinistic pathogens
o Saprophytes

4. Obligate Parasites
• Mycobacterium tuberculosis complex
Contains M. tuberculosis, M. bovis, M. africanum, M. microti, M. canetti, M. caprae
and M. pinnipedii
• Mycobacterium leprae

5. Opportunistic Pathogens
Non-tuberculosis mycobacteria (NTM)
This group contains mixed group of isolates from diverse sources: birds, cold-blooded
and warm-blooded animals, from skin ulcers, and from soil, water and other
environmental sources.
They are opportunistic pathogens and can cause many types of disease.

6. Pathogenesis
Source of infection:
 Open case of pulmonary tuberculosis
Mode of infection
 Direct inhalation of aerosolized bacilli contained in the droplet nuclei of expectorated sputum.
 Infection also occurs infrequently by ingestion for example, through infected milk, and rarely
by inoculation.

7. Transmission of M.tuberculosis
Millions of tubercle bacilli in lungs (mainly in cavities).
Coughing projects droplet nuclei into the air that contain
tubercle bacilli.
One cough can release 3,000 droplet nuclei.
One sneeze can release tens of thousands of droplet nuclei

8. Infection
The initial infection with M. tuberculosis is referred to as a
 Primary infection
Subsequent disease in a previously sensitized person, either from an exogenous source or
by reactivation of a primary infection is known as
 Postprimary tuberculosis
Both forms exhibit quite different pathological features.

9. Difference b/w Primary and Postprimary
tuberculosis
Characteristics Primary Postprimary
Site Any part of
lung
Apical region
Local lesion Small Large
Cavity formation Rare Frequent
Lymphatic
involvement
Yes Minimal
Infectivity* Uncommon Usual
Local spread Uncommon Frequent
*Pulmonary cases

10. Immunology
Tubercle bacilli do not contain or secrete a toxin.
The exact basis of their virulence is not understood, but
seems to be related to their ability to survive and multiply
in macrophages.
Humoral immunity appears to be irrelevant.
The only specific immune mechanism effective is the CMI.

11. The key cell is the activated CD4+ helper T cell which can develop along two
different paths: The Th1 and Th2 cells
Th1 dependent cytokines activate macrophages, resulting in protective immunity
and containment of the infection
Th2 cytokines induce delayed type hypersensitivity (DTH), tissue destruction and
progressive disease

12. Laboratory Diagnosis
Specimen Collection
Type of lesion Specimen
Pulmonary tuberculosis Sputum
 Early morning sputum samples should be collected for 3
consecutive days in a sterile container
 In case of renal tuberculosis, 3-6 morning urine samples
should be collected
Laryngeal swabs or
bronchial washings
Gastric lavage
Renal tuberculosis Urine
Tuberculosis meningitis CSF

13. Direct Microscopy
 Ziehl-Neelsen staining (hot staining method)
 Kinyoun’s method (cold staining method)
 Acid fast bacilli resist decolourisation with acid and alcohol
once they have been stained with carbolfuchsin.
 AFB appear as pink, long, slender bacilli with beaded
appearance.
Ziehl-Neelsen Staining

14. Fluorescent staining by Auramine O or auramine rhodamine
Mycobacterium spp. will fluoresce yellow against dark background under fluorescent microscope

15. Culture
 Concentrated specimen is inoculated
on Lowenstein – Jensen’s medium and
incubated at 370C for 2 – 8 weeks
 Colonies appear as buff coloured, dry,
irregular colonies with wrinkled surface
and not easily emulsifiable
(Buff, rough and tough colonies)
 Colonies are creamy white to yellow colour
with smooth surface and easily emulsifiable

16. Detection of antibodies
 Various methods such as enzyme linked immune sorbent assay (ELISA), radio immunoassay (RIA), latex
agglutination assay have been employed for detection of antibodies in patient serum.
 However, diagnostic utility of these methods is doubtful.
 WHO has recommended that these tests should not be use for diagnosis of active tuberculosis.