Mycobacterium Tuberculosis

What sample is needed for the Mantoux test?

• This test is done on the patient’s skin.

What are the indications for the Mantoux test?

1. To diagnose a suspected case of tuberculosis.
2. Screening of people at risk like:
   1. Health worker.
   2. Immigrant to a high-risk area.
   3. IV drug user.
   4. Patients at increased risk of developing active TB.
3. So, this TT should be targeted to the high-risk group, which is called targeted tuberculin testing, rather than people at low risk, which is called screening testing.

What is the epidemiology of Mycobacterium Tuberculosis?

1. Tuberculosis is the second leading cause of od death in the world.
   1. Nearly 3 million people die each year.
   2. 7% of all deaths occur worldwide.
   3. The global epidemic may become worse because of drug-resistant organisms and HIV patients.
2. Mycobacteria are widely distributed worldwide. They are referred to as acid-fast bacilli because they resist decolorization after being mordanted with strong acid.
   1. The staining property is related to the cell wall composition with high lipid contents.
   2. The acid-fastness results from the formation of complexes between the dye and mycolic acid, one of the cell wall lipids.

Mycobacterium tuberculosis: TB pathogenesis for type IV

What are the laboratory characteristics of Mycobacterium tuberculosis?

1. They are weakly gram-positive organisms.
2. M. tuberculosis measures 0.2 to x 5.0 µm bacillus.
3. These are slender, beaded bacilli and non-sporing organisms.
4. It is an obligate aerobe.
5. It grows in high O2 tension (pO₂) areas like the lung apex tissue.
6. It is a slow-growing organism that needs 1 to 2 weeks or more to grow.
7. It has high cell-walled lipid content like mycosides and is impervious to gram stains.
   1. Smears are treated with concentrated carbol fuchsin for 10 to 20 minutes, which acts as a mordant by heating, and then decolorized with 20% sulphuric acid+ alcohol; now, bacilli will have a bright red color.

Mycobacterium Tuberculosis: Acid-fast tuberculous bacilli

What are the culture media for Mycobacterium Tuberculosis?

1. These bacteria need highly enriched media, Lowenstein-Jensen media. These bacteria do not grow on ordinary media.
2. Lowenstein-Jensen media contains whole eggs, aspargine, glycerol, and malachite green, inhibiting contaminants’ growth.
3. The specimen is incubated at 37 °C for 2 to 3 weeks, but the culture should be kept for 6 to 8 weeks.
4. Nowadays, these bacteria are identified under fluorescent microscopy.
5. These are divided into two groups:
   1. Rapid grower, which forms the colonies in 2 to 3 days.
   2. A slow grower who takes 2 to 3 weeks.
6. The medically important mycobacteria are:
   1. M. tuberculosis.
   2. M. bovis.
   3. M. leprae.
   4. Atypical mycobacteria.
7. Mycobacteria tuberculosis causes a slowly progressive chronic infection, usually of the lungs.
   1. However, other organs are not spared by this disease.
   2. The primary source is the lung’s secretions, so-called open disease.

Mantoux test:

What is the principle of the Tuberculin sensitivity test (TT) and the Mantoux test?

1. The Tuberculin test (TT) is important in diagnosing and preventing tuberculosis.
   1. This test is more sensitive than the X-ray chest.
2. This test is done on the patient, in which purified protein derivatives (PPD) are stabilized by Tween 80 (polysorbate 80-coated nanoparticles) injected into the skin (Intradermal).
   1. The standard test material is intermediate-strength, 5 tuberculin units, PPD.
3. Lymphocytes will recognize PPD as an antigen and give rise to type IV, cell-mediated reaction.

4. There will be a local inflammatory reaction in a person who has TB or has past exposure to TB.
5. This test will give a severe reaction in the case of active TB or patients with vaccination. The skin may slough.

How would you read the Tuberculin test (TT) or Mantoux test:

1. Read the test area after 48 to 72 hours of the injection.
2. The negative case is when there is no induration.
3. In positive cases, there will be induration at the site of injection appearing in 48 to 72 hours.

What are the criteria of the American Thoracic Society and CDC?

1. They suggest the following criteria for different population groups:
2. Induration <5 mm Diameter is seen in:
   1. HIV patients or immunodeficiency state.
   2. Or a patient with a CMI defect.
   3. Close contact with active TB case.
   4. The patient had an X-ray finding of old TB.
   5. Patients with fibrosis or calcification in the lung suggest previous pulmonary tuberculosis.
3. Induration >10 mm in Diameter seen in:
   1. I/V drug users.
   2. Nursing home residents.
   3. The traveler from the endemic or high-risk area of Tuberculosis, prisoners, homeless,  I/V drug abusers, and other chronically ill patients.
   4. A worker in the home care facility.
   5. Malnutrition, postgastrectomy, steroid use, and Diabetes.
4. Induration >15 mm in diameter seen in:
   1. Patient with active TB.
   2. All patients who don’t fulfill the above criteria.
5. A booster reaction may be mistaken for conversion among hospital workers or other people where repeated testing is needed.
6. In cases where the primary reaction is negative, or the result is in doubt, give the second dose after one week.
7. If the size of the induration is increased by more than 6 mm next year, a new tuberculous infection may be suggested.

What are the contraindications for the Tuberculin and Mantoux skin tests (T T)?

1. A patient who has active TB will have a very severe reaction.
2. A patient who has a vaccination with Bacillus Calmette Guerin (BCG).
3. No use in a malnourished patient.

Where will you see the positive Tuberculin and Mantoux skin tests (TT)?

1. An active case of TB.
2. Other types of Mycobacterial infection.

Where will you see a negative Tuberculin or Mantoux skin test (TT)?

1. Immune incompetent chronically ill patient.
2. The patient was not exposed to TB.
3. It is found that 20% of the HIV-negative and 40% of HIV-positive cases have tuberculosis.
4. Viral infections, including measles and rubella, can suppress tuberculin reactivity. However, this effect is transient.

• Because the tuberculin skin test is limited in sensitivity and specificity, new methods, such as a sandwich-capture enzyme-linked immunoabsorbent assay, are being developed to diagnose Mycobacterium tuberculous infection.

Questions and answers: