Mycobactreium Tuberculosis

INTRODUCTION:
  • First isolated by Robert Koch
  • Mycobacterium tu
    berculosis infection in humans is most commonly because of inhalation
  • It is a non- sporing, aerobic, gram negative bacteria that measures 0.5-3 micon m
  • Spheroplasts and L forms are seen
  • Cell wall has 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) and lipoarabinomannan (LAM), a lipid polysaccharide complex extending from the plasma membrane to the surface forming waxy coat
  • The single most common cause of pyrexia of unknown origin 
  • Mycobacterium tuberculosis complex 
  1. 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 
  2. 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:
  1. Delayed-type hypersensitivity (DTH) (eg.Phlyctenular keratoconjunctivitis)
  2. Cell-mediated immunity (CMI)
TYPING METHOD:
  • Bacteriophage typing
  • Bacteriocin typing
  • Molecular typing
  1. 156110 RFLP typing - gold standard
  2. Spoligotyping (spacer oligotyping)
  3. Reaction Positive in Negative in
    Niacin M.tuberculosisM. simiaeM.cheloneii M.bovis
    Nitrate reduction M.tuberculosis M.bovis
    Aryl sulphatase EtCatalase test Atypical mycobacteria M.tuberculosis
    Peroxidase test Tubercle bacillus Atypical mycobacteria
    Neutral red test Virulent strains Avirulent strains
Exam Question
  • M.tuberculosis, M.bovis, M. bovis bacille Calmette-Guerin (BCG), M.africanum, M.microti, and M.canettii forms mycobacterium tuberculosis complex
  • Type IV hypersensitivity to Mycobacterium tuberculosis antigen may manifest as Phlyctenular keratoconjunctivitis
  • Cell wall of M.tuberculosis has high lipid content 
  • Mycolic acids and LAM in M.tuberculosis form waxy coat
  • M.tuberculosis Lacks exotoxins or endotoxin
  • M.tuberculosis is a non- sporing, aerobic, gram negative bacteria that measures 0.5-3 micon m
  • The normal time required to culture mycobacterium TB is 4-8 weeks
  • Mycobacterium tuberculosis was discoverd by Robert koch
  • The medium used for Mycobacterium tuberculosis is Lowenstein jensen medium
  • Mycobacterium tuberculosis is niacin positive
  • The single most common cause of pyrexia of unknown origin is Mycobacterium tuberculosis
  • Mycobacterium tuberculosis infection in humans is most commonly because of inhalation
  • Live TB bacilli culture is by MGIT

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