Wednesday, August 29, 2012

Mycobacterium Tuberculosis photo blog

Mycobacterium tuberculosis is a dangerous bacterium. If your immunity gets low for any reason you can acquire it. The organism can remain dormant for years only to reappear later in life and wreak havoc!


Organisms:
The pathogenic organisms are: Tuberculosis, Bovis, Leprae, Avium complex, Fortuitum complex, Kansasii, Marinum and many others

Morphology:
These are Aerobic organisms in the shape of bacilli (rods). Mycobacterium tuberculosis ranges in length between 2 - 4 microns, and a width between 0.2 - 0.5 microns.




Reproduction:
Apart from Fortuitum all mycobacteria is slowly growing. Growth in a culture medium takes place in 8 weeks.
Mycobacterium Fortuitum on skin of patient:


Transmission:
Mycobacterium tuberculosis is transmitted via respiratory droplets (aerosol) from person to person. This is because tuberculosis is only present in humans and no other species, except cattle which are infected by mycobacterium bovis. Mycobacterium bovis causes abdominal tuberculosis and it spreads by drinking infected milk.

Pathogenesis:
Mycobacterium tuberculosis causes disease in humans by preventing fusion of lysosome with phagosome. Primary lesions occur in lower lobes of lung while repetitive lesions occur in apices of lung, kidney, brain or  bone.

Video: Demonstrating transmission, pathogenesis and granuloma formation:



Microscopic Pathology:
Initially the lesion is exudative later on becomes granulomatous in which there is central giant cells containing tubercle bacilli surrounded by zone of epithelioid cells.



Gross Pathology:

  • Lungs: Cavitation due to tuberculosis. Patient will present with chronic cough and cachexia.



    • Miliary tuberculosis of Lung: Spreads like millet seeds

  • Lymph Nodes: Condition is called scrofula. The picture shows typical appearance of matted lymph nodes with caseating material inside.




  • Kidney: Beware of sterile pyuria.


    • Miliary tuberculosis of Kidney:

  • Brain: Tuberculosis in the basilar area. All the signs of meningitis will be there.




  • Epidydimis:




  • Bone: Initially intervertebral discs and later surrounding vertebral bodies are destroyed by infection



  • Small Intestine: Commonly produces strictures and is mainly caused by drinking milk infected with mycobacterium bovis from cows or from swallowing sputum having mycobacterium tuberculosis in it.


  • Spleen:



    • Miliary Tuberculosis of Spleen:

  • Pericardium:




  • Tuberculosis of thoracic aorta: Apparently this photograph, courtery of Yale Rosen, M.D. from Atlas of Granulomatous Diseases , shows spread of tuberculosis into thoracic aorta and causing massive intrapulmonary haemorrhage.



Diagnosis:

  • They stain red with carbol fuschin stain (component of Ziehl-Neelsen stain) because of high lipid thus called acid fast:


  • Ziehl-Neelsen stain of Mycobacterium Leprae:

  • Auramine and rhodamine fluorescent stain:





  • A sputum sample stained with fluorescent auramine with acridine orange counterstain:





  • Culture on Lowenstein jenson medium: takes 8 weeks to grow!



    • Culture on Lowenstein jenson medium showing typical clumped colonies, higher magnification:



  • Diagnosis with DNA (Gene) probes:





  • Diagnosis with Polymerase Chain Reaction:





  • Mantoux test (Purified Protein Derivative) evaluation: The three sizes can be 5mm or more, 10mm or more and 15mm or more. This test has limited value.



Treatment:

According to WHO the recommended doses for the routinely used drugs for treatment of tuberculosis in children are:


  • Isoniazid: 10-15 mg/kg (maximum 300mg/day)
  • Rifampicin: 10-20 mg/kg (maximum 600 mg/day)
  • Pyrazinamide: 30-40 mg/kg
  • Ethambutol: 15-25 mg/kg


Source of images: CDC, Atlas of Granulomatous Diseases by Yale Rosen, M.D., Wikipedia










No comments:

Post a Comment