Mycobacterium Tuberculosis (TB)

 Mycobacterium Tuberculosis (TB):  ( Acid fast bacilli).

Introduction 

TB is an infectious disease that usually affects the lungs TB is commonly called contagious infection that usually attacks the lungs, hence it is also called as Respiratory Tract Infection. It can also spread to other parts of the body like brain and spine, a type bacteria called Mycobacterium Tuberculosis. The bacteria that cause TB is spread through the air from person to person when a person comes in contact with TB disease cough, speaks, or sings, people nearby may breath these bacteria and get infected. The selective media is Lowenstein- Jensen (LJ) medium.

Two types of TB conditions.

1. Classification 

Kingdom: Bacteria 

Phylum: Actinobacteria 

Order: Actinomycetales

Family: Mycobacteriaceae

Genus: Mycobacterium 

Species: M. Tuberculosis.

Morphology 

1. Small, aerobic, non-motile bacillus.
2. It is rod-shaped.
3. Non-capsulated.
4. Non-sporing.
5. Mycobacteria have an outer membrane lipid bilayer. This high lipid content of the pathogenesis accounts for it's unique clinical characteristics.
6. If the gram-stain weakly gram positive or does retain dye as a result of high lipid and mycolic acid content of it's cell wall.
7. Mycolic acids are long fatty acid found in the cell wall. Mycolic acids are major and specific lipid components of the mycobacteria cell envelope and are essential for survival of the bacteria.
8. Mycolic acids have unique properties and make the organism more resistant to chemical damage and dehydration and limit the effectiveness of hydrophilic antibiotics.
9. It divides every 16-30 hours which is extremely slow rate compared to other bacteria.
10. Mycobacterium species are classified as acid-fast bacteria due to their impermeability to certain dyes and stains.
11. Acid-fast staining is also known as Ziehl Nielsen staining. When this method is used the MTB smear is fixed, stained with carbolfuchsin (pink dye) and decolourised with acid alcohol. The smear is counter stained with methylene blue or certain other dyes. 
12. Acid fast bacilli appear bright red or pinkish in a contrasting background.
13. Mycobacterium Tuberculosis is strictly aerobic bacterium. It therefore multiplies better in pulmonary tissue than in the deeper organs.

Clinical Manifestation ( signs & symptoms)

TB bacteria most commonly grows in the lungs and can caused symptoms such as:

1. A bad cough that lasts 3 weeke or longer.
2. Pain in the chest.
3. Coughing up blood or sputum.
4. Unintentional weight loss.
5. Fatigue, fever, chills.
6. Night sweats, loss of appetite.

Pathogenesis 

1. TB injection begins when the mycobacteria reach the alveolar air sacks of the lungs, where they invade and replicate within the alveolar macrophages.
2. Macrophages identify the bacterium as foreign and attempt to eliminate it by phagocytosis.
3. During this process, the bacterium is enveloped by this macrophages and stored temporarily in the membrane bound vesicle called a phagosome.
4. The phagosome then combines with a lysosome to create a phagolysosome.
5. In the phagolysosome, the cell attempts to use reactive oxygen species and acid to kill bacterium.
6. However, M. Tuberculosis has a thick, waxy mycolic acid capsule that protects it from these toxic substances.
7. M. Tuberculosis is able to reproduce inside the macrophages and will eventually kill the immune cell.
8. The primary site of infection in the lungs, know as the "Ghon focus", is generally located in either the upper part of the lower lobe, or the lower part of the upper lobe.
9. "Ghon focus", is a primary lesion caused by MTB developed in lung. It is name after an Austrian pathologist ANTON GHON.

Tuberculosis Transmission 

• When someone who has TB coughs, sneezes, talks, laughs, or sings, they release tiny droplets that contain the germs.
• If you breath in these germs, you can get it.
• TB isn't easy to catch. You usually have to spend a long time around someone who has a lot of the bacteria in their lungs. 
• You're most likely to catch it from co-workers, friends and family members.
• Tuberculosis germs don't thrives on surface. You can't get it from shaking hards with someone who has it or by sharing their food or drink.

Cultural characteristics of Mycobacterium Tuberculosis in Lowenstein- Jensen (LJ) medium.

1. It is an egg based medium and growth is quite slow.
2. It takes 6-8 weeks to get visual colonies on this type of media.
3. Colonies are non-pigmented, dry rough, raised l, irregular with wrinkled surface.
4. They are creamy white initially, becoming yellowish or buff colored on further incubation.
5. Growth is ergonomic ( grows more luxuriantly in culture). 
6. Optimum temperature is 35-37°C and optimum pH is 6.4 to 7.
7. The green colour of the medium is due to the presence of malachite green which is one of the selective agents to prevent growth of most other contaminates.
8. A faster result can now be obtained using Middle brook medium 7H11 or BACTEC.
9. It is distinguished from other mycobacteria by its production of catalase and niacin.
10. Other tests to confirm its identity include gene probes and MALDI-TOF.
11. In mass spectroscopy, Matrix- assisted laser desorption/ ionization (MALDI) is an ionization technique that uses a laser energy absorbing matrix to create ions from large molecules with minimal fragmentation.

Diagnosis 

1. To check for TB, a doctor will use a stethoscope to listen to the lungs and check for swelling in the lymph nodes. They will also ask about symptoms and medical history as well as assessing the individual's risk of exposure to TB.
2. A chest x-ray is done patches in lungs. Multiple sputum culture for acid-fast bacilli evaluation.
3. TB is most commonly diagnosed via a skin test involving an injection in the forearm.
4. The most common diagnostics test for TB is a skin test (also called a MANTOUX SKIN TEST or tuberculin skin test) where a small injection of PPD tuberculin, an extract of the TB bacterium, is made just below the inside forearm.
5. Partially purified antigen prepared by ammonium sulphate fractionation technique. 
6. Tuberculin (also called purified protein derivative or PPD) is the solution used to administer the test. The preferred term for the test is tuberculin skin test, or TST.
7. The injection site should be checked after 2-3 days and if a hard, red bump has swollen up to a specific size, then it is to a specific size, then it is likely that TB is present.
8. Unfortunately, the skin test is not 100 percent accurate and has been known to give incorrect positive and negative readings.
9. [ Nucleic acid amplification tests and adenosine deaminase testing may allow rapid diagnosis of TB]. They are molecular diagnostics techniques. These tests, however, are not routinely recommended, as they rarely after how a person is treated and are very expensive.
10. Blood tests to detect antibodies are not specific or sensitive, so they are not recommended.

Prophylaxis and Prevention 

The precise type and length of antibiotics treatment depends on a person's age,..

• Over all health,
• Potential resistance to drugs,
• Whether the TB is latent or active, 
• And the location of infection (i.e, the lungs, brain, kidneys)

1. People with latent TB may need just one kind of TB antibiotics, whereas people with active TB (particularly MDR-TB) will often require a prescription of multiple drugs.
2. Antibiotics [ isoniazid INH ] are usually required to be taken for a relative long time. The standard length of time for a course of TB antibiotics is about 6 months.
3. Vaccinations:- In countries where Tuberculosis is more common, infants often are vaccinated with Bacillus Calmette - Guerin (BCG) vaccine because it can prevent severe tuberculosis in children.
4. Keeping immune system strong.
5. Balanced diet.
6. Keeping body hydrated by drinking lots of water or fluids.