Mycobacterium Tuberculosis

INTRODUCTION:

• First isolated by Robert Koch
• Infection in humans is most commonly because of inhalation
• The single most common cause of pyrexia of unknown origin 

• It is a non- sporing
• aerobic
• gram negative bacteria 
• measures 0.5-3 micon m
• Spheroplasts and L forms are seen

Cell wall:

•  high lipid content (more than 60% of the total cell wall mass)
• Long-chain fatty acids called mycolic acids (for which the mycobacteria are named) 
• lipoarabinomannan (LAM)
• Lipid polysaccharide complex extending from the plasma membrane to the surface forming waxy coat
• Mycobacterium tuberculosis complex 
• Organisms are obligate pathogens which display >95% DNA / DNA homology:
• M.tuberculosis, M.bovis, M. bovis bacille Calmette-Guerin (BCG), M.africanum, M.microti, and M.canettii
• Like all microbacteria, members of the M.tuberculosis complex are aerobic, non-spore-forming, non-motile, slightly curved or straight roads

CULTURE MEDIA:

• Semisynthetic agar media
• Inspissated egg media
  •  LJ medium without starch (mc used)
• Dorset’s egg
  • Buff, rough, tough colonies 
• Broth media
• Live TB bacilli culture is by MGIT
• The normal time required to culture mycobacterium TB is 4-8 weeks

ANTIGENS:

• Lipids – mycolic acid, cord factor
• Proteins – responsible for tuberculin reaction
• Polysaccharides – responsible for immediate type of hypersensitivity

VIRULENCY:

• Mycolic acid – also responsible for acid fastness, granuloma formation
• Cord factor
• Lipoarabinomannan (sulfolipid)  prevents fusion of phagosome with lysosome inside macrophages à  intracellular survival
• M.tuberculosis heat shock protein
• Mycobacteria do not produce classic exotoxins or endotoxins.
•  Disease processes are thought to be the result of two related host responses:
  • Delayed-type hypersensitivity (DTH) (eg.Phlyctenular keratoconjunctivitis)
  • Cell-mediated immunity (CMI)

TYPING METHOD:

• Bacteriophage typing
• Bacteriocin typing
• Molecular typing

1. 156110 RFLP typing – gold standard
2. Spoligotyping (spacer oligotyping)

Reaction	Positive in	Negative in
Niacin	M.tuberculosis M. simiae M.cheloneii	M.bovis
Nitrate reduction	M.tuberculosis	M.bovis
Aryl sulphatase Et Catalase test	Atypical mycobacteria	M.tuberculosis
Peroxidase test	Tubercle bacillus	Atypical mycobacteria
Neutral red test	Virulent strains	Avirulent strains

Don’t Forget to Solve all the previous Year Question asked on Mycobacterium Tuberculosis
Click Here to Start Quiz