pbl 2 –pod 1 : the morphology and structure of mycobacterium tuberculosis, the tests required for...

A S E M S H A D I D

PBL 2 –POD 1

OBJECTIVES :

• Describe the morphology and structure of mycobacterial tuberculosis ?

• What are the tests required for mycobacterial infection :• Mantoux skin test• Sputum examination using Ziehl-Neelsen staining• Sputum culture using lowenstien-jensen media• Discuss the clinical features and transmission of

mycobacterial tuberculosis.• What are the pathological changes in mycobacterium

tuberculosis? • How to control mycobacterial infection in the environment

and vaccine available?

DESCRIBE THE MORPHOLOGY AND STRUCTURE OF MYCOBACTERIUM TUBERCULOSIS ?

• Mycobacterium is a genus of Actinobacteria , given its own family, the Mycobacteriaceae.

• ( Actinobacteria are a group of Gram-positive bacteria )

• The genus includes pathogens known to cause serious diseases in mammals, including tuberculosis (Mycobacterium tuberculosis) .

• Mycobacteria are Gram-resistant (waxy cell walls rich in lipid), non-motile.

• Mycobacteria are aerobic ( use o2 ) and nonmotile bacteria , that are characteristically acid-alcohol-fast.

• Acid-fastness is a physical property of certain bacteria

• Acid-fast organisms are difficult to characterize using standard microbiological techniques (e.g. Gram stain )

MYCOBACTERIA ASSOCIATED WITH HUMAN DISEASE

Mycobacterium Environmental contaminant Reservoir

M tuberculosis No Human

M bovis No Human, cattle

M leprae No Humn

M kansasii Rarely Water, cattle

M marinum Rarely Fish, water

M scrofulaceum Possibly Soil, water

M avium intracellulare

Possibly Soil, water, birds

M ulcerans No Unknown

M fortuitum Yes Soil, water, animals

M chelonae Yes Soil, water, animals

Mycobacterium tuberculosis

Mycobacterium tuberculosis is a pathogenic bacterial species in the family Mycobacteriaceae and the causative agent of most cases of tuberculosis.

Schematic diagram of Mycobacterial cell wall.

1. outer lipids2. mycolic acid3. polysaccharides (arabinogalactan)4. peptidoglycan5. plasma membrane6. lipoarabinomannan (LAM)7. phosphatidylinositol mannoside8. cell wall skeleton

What are the tests required for mycobacterial infection :

• The Mantoux test or Mendel-Mantoux test Also known as: Purified Protein Derivative; PPD; Mantoux , is a screening tool for tuberculosis (TB) .

What does the test result mean?

A positive result will form a red and swollen circle at the site of the injection.

a positive tuberculin skin test, an immune reaction to a small quantity of tuberculosis antigens

A negative result for either test means that it is likely that the person tested does not have a TB infection.

The Mantoux skin test consists of an intradermal injection of one-tenth of a milliliter (ml) of PPD tuberculin.

The Ziehl–Neelsen stain, also known as the acid-fast stain AFB Acid-Fast Bacillus .

t is a special bacteriological stain used to identify acid-fast organisms, mainly Mycobacteria. Mycobacterium tuberculosis is the most important of this group because it is responsible for tuberculosis (TB) السل .

• Acid-fastness is a physical property of certain bacteria

• Acid-fast organisms are difficult to characterize using standard microbiological techniques (e.g. Gram stain )

A negative AFB smear may mean that no infection is present, that symptoms are caused by something other than mycobacteria

What does the test result mean?

Positive AFB smears indicate a probable mycobacterial infection.

Mycobacterium tuberculosis (stained red) in tissue (blue).

• LJ medium is A growth medium called also The Löwenstein–Jensen medium.

• A growth medium or culture medium is a liquid or gel designed to support the growth of microorganisms There are different types of media for growing different types of cells.

• LJ medium specially used for culture of Mycobacterium, mostly the Mycobacterium tuberculosis.

• When grown on LJ medium, M. tuberculosis appears as brown

Löwenstein-Jensen medium used for growing M. tuberculosis in a McCartney bottle.

Uses

For diagnosis of Mycobacterial infectionsFor testing antibiotic aptly of isolatesFor differentiating different species of mycobacterium

Discuss the clinical features and transmission of mycobacterial

tuberculosis.

• TB is an airborne - جوا disease caused by the bacterium - محمولMycobacterium tuberculosis (M. tuberculosis) .

• Tuberculosis kills 3,000,000 people in the world every year, more than AIDS

• How is TB diagnosed?

Symptoms of tuberculosis include:

1. Fever2. Night-time sweating3. Loss of weight4. Persistent cough5. Constant tiredness6. Loss of appetite

• Diagnosis of tuberculosis is made by :

1. a positive tuberculin skin test2. It can be confirmed by X rays of the chest 3. microscopic examination of sputum4. Detection of significant numbers of acid-fast bacilli (using the Ziehl-Neelsen

stain)5. laboratory culture of the bacterium

Transmission of TB :

M. tuberculosis is carried in airborne particles, called droplet nuclei, of 1– 5 microns in diameter.

Infectious droplet nuclei are generated when persons who have pulmonary or laryngeal TB disease cough, sneeze, shout, or sing. It can also occur through the gastrointestinal tract

Depending on the environment, these tiny particles can remain in the air for several hours.

M. tuberculosis is transmitted through the air, not by surface contact.

• Young children with pulmonary and laryngeal TB disease are less likely than adults to be infectious.

What are the pathological changes in mycobacterium

tuberculosis?

Droplet nuclei containing tubercle bacilli are inhaled, enter the lungs, and travel to the alveoli.

Tubercle bacilli multiply in the alveoli.

A small number of tubercle bacilli enter the bloodstream and spread throughout the body. The tubercle bacilli may reach any part of the body, including areas where TB disease is more likely to develop (such as the brain, larynx, lymph node, lung, spine, bone, or kidney).

Within 2 to 8 weeks, special immune cells called macrophages ingest and surround the tubercle bacilli. The cells form a barrier shell

called a granuloma . is an inflammation found in many diseases. It is a collection of immune cells known as macrophages.

If the immune system cannot keep the tubercle bacilli under control, the bacilli begin to multiply rapidly (TB disease).

How to control mycobacterial infection in the environment

and vaccine available?

VACCINATION SCHEDULE IN SAUDI ARABIA?