Mycobacteria

Question 1

TB was documented in:
Egypt

Answer 1

5,000 yrs ago

Question 2

TB was documented in:
India

Answer 2

3,000 yrs ago

Question 3

TB was documented in:
China

Answer 3

2,300 yrs ago

Question 4

seventh place in the global ranking of causes of death

every 15 seconds someone in the world dies from it

Answer 4

Tuberculosis

Question 5

Thin, Straight, rod-shaped, obligate aerobe, no spores.
Resist decolorization by acid or alcohol and are therefore called “acid-fast” bacilli.

Answer 5

Mycobacteria

Question 6

Causes tuberculosis.

Answer 6

Mycobacterium tuberculosis

Question 7

causes leprosy.

Answer 7

Mycobacterium leprae

Question 8

Although they do not stain readily, once stained they resist decolorization by acid or alcohol and are therefore called

Answer 8

Acid fast

Question 9

infects people with AIDS, immunocompromised persons

Answer 9

Mycobacterium avium-intracellulare (M avium complex, or MAC) and other atypical mycobacteria

Question 10

BCG - Bacille Calmette-Guérin

Answer 10

M. tuberculosis
M. leprae

Question 11

AIDS patient

Answer 11

M. avium complex

Question 12

Bacteria are classified in the genus Mycobacterium on the basis of

Answer 12

their acid-fastness,
the presence of mycolic acids containing 70 to 90 carbons, and
a high (61% to 71 mol%) guanine plus cytosine (G+C) content in their deoxyribonucleic acid (DNA)

Question 13

Mycobacteria cell wall

Answer 13

possess a complex, lipid-rich
The basic structure of the cell wall is typical of gram-positive bacteria: an inner plasma membrane overlaid with a thick peptidoglycan layer and no outer membrane
This cell wall is responsible for many of the characteristic properties of the bacteria (e.g., acidfastness; slow
growth; resistance to detergents,common antibacterial antibiotics, and the host immune response; antigenicity).

Question 14

What are Anchored in the plasma membrane of mycobacterial cell wall

Answer 14

proteins, phosphatidylinositol mannosides, and lipoarabinomannan (LAM).

Question 15

is functionally related to the O-antigenic lipopolysaccharides present in other bacteria.

Answer 15

lipoarabinomannan (LAM)

Question 16

Mycobacterium cell wall

Answer 16

Additional lipids, glycolipids, and peptidoglycolipids are also present. The lipid components comprise 60% of the cell wall weight.
Transport proteins and porins are interspersed throughout the cell wall layers, and these constitute 15% of the cell wall weight.
The proteins are biologically important antigens, stimulating the patient’s cellular immune response.
Extracted and partially purified preparations of these protein derivatives (purified protein derivatives [PPDs]) are used as skin test reagents to measure exposure
to M. tuberculosis.

Question 17

Constituents of Tubercle Bacilli

Answer 17

Lipids: Mycolic acids, waxes, and phosphatides.
Virulent strains: cord factors

Question 18

cause: granuloma formation;
- induce caseous necrosis.
- acid-fastness.

Answer 18

Lipids: Mycolic acids, waxes, and phosphatides.

Question 19

inhibits migration of leukocytes, causes chronic granulomas, and can serve as an immunologic “adjuvant.”

Answer 19

Virulent strains: “cord factor” (trehalose-6,6’-dimycolate)

Question 20

Lipids

Answer 20

Mycobacteria are rich in lipids.
These include mycolic acids (long-chain fatty acids C78–C90), waxes, and phosphatides.
In the cell, the lipids are largely bound to proteins and polysaccharides.
Muramyl dipeptide (from peptidoglycan) complexed with mycolic acids can cause granuloma formation; phospholipids induce caseous necrosis.
Lipids are to some extent responsible for acid-fastness.
Their removal with hot acid destroys acid-fastness, which depends on both the integrity of the cell wall and the presence of certain lipids. Acid-fastness is also lost after sonication of mycobacterial cells. Analysis of lipids by gas chromatography reveals patterns that aid in classification of different species.

Question 21

Cord factor

Answer 21

is a mycoside formed by the union of 2 mycolic acids with a disaccharide (trehalose). This mycosideis only found in virulent strains of Mycobacterium tuberculosis. Its presence results in parallel growth of the bacteria, so they appear as cords. Exactly how the virulence occurs is still unknown, but experiments show that cord factor inhibits neutrophil migration and damages mitochondria. Its injection into mice results in the release of tumor necrosis factor (TNF or cachectin), resulting in rapid weight loss.

Question 22

Virulent strain

Answer 22

Virulent strains of tubercle bacilli form microscopic “serpentine cords” in which acid-fast bacilli are arranged in parallel chains. Cord formation is correlated with virulence. A “cord factor” (trehalose-6,6’-dimycolate) has been extracted from virulent bacilli with petroleum ether. It inhibits migration of leukocytes, causes chronic granulomas, and can serve as an immunologic “adjuvant.”

Question 23

Protein

Answer 23

Proteins
Each type of mycobacterium contains several proteins that elicit the tuberculin reaction. Proteins bound to a wax fraction can, upon injection, induce tuberculin sensitivity. They can also elicit the formation of a variety of antibodies.

Question 24

Polysaccharides

Answer 24

Mycobacteria contain a variety of polysaccharides. Their role in the pathogenesis of disease is uncertain. They can induce the immediate type of hypersensitivity and can serve as antigens in reactions with sera of infected persons.

Question 25

Constituents of Tubercle Bacilli

Answer 25

Sulfatides
Proteins
Polysaccharides
Wax D

Question 26

mycosides that resemble cord factor with sulfates attached to the disaccharide. Inhibit the phagosome from fusing with the lysosome

Answer 26

Sulfatides

Question 27

elicit the tuberculin reaction, tuberculin sensitivity and elicit the formation of a variety of antibodies.

Answer 27

Proteins

Question 28

: induce the immediate type of hypersensitivity and can serve as antigens in reactions with sera of infected persons.

Answer 28

Polysaccharides

Question 29

complicated mycoside that acts as an adjuvant

Answer 29

Wax d

Question 30

produce pigment in light but not in darkness;

Answer 30

Photochromogens

Question 31

develop pigment when growing in the dark;

Answer 31

Scotochromogens

Question 32

are nonpigmented or have light tan or buff-colored colonies.

Answer 32

Nonchromogens

Question 33

enhances antibody formation to an antigen)
and may be the part of Mycobacterium tuberculosis that activates the protective cellular immune system.

Answer 33

Adjuvant

Question 34

The Runyon classification scheme of NTM
3 groups

Answer 34

slow-growing photochromogens
slow-growing scotochromogens
slow-growing non pigment

Question 35

Facultative intracellular growth:

Answer 35

With the first exposure (usually by inhalation into the lungs), the host has no specific immunity. The inhaled bacteria cause a local infiltration of neutrophils and macrophages. Due to the various virulence factors, the phagocytosed bacteria are not destroyed. They multiply and survive in the macrophages. The bacteria cruise through the lymphatics and blood to set up camp in distant sites. This period of facultative intracellular existence is usually short-lived because the host rapidly acquires its prime defense against the acid-fast buggers: cell-mediated immunity.

Question 36

Cell-mediated immunity:

Answer 36

Some of the macrophages succeed in phagocytosing and breaking up the invading bacteria. These macrophages then run toward a local lymph node and present parts of the bacteria to T-helper cells. The sensitized T-cells then multiply and enter the circulation in search of Mycobacterium
tuberculosis. When the T-cells encounter their antigenic target, they release lymphokines that serve to attract macrophages and activate them when they arrive. These activated macrophages can now destroy the bacteria. It is during this stage that the macrophage attack actually results in local destruction and necrosis of the lung tissue. The necrosed tissue looks like a granular creamy cheese and is called caseous necrosis. This soft caseous center is surrounded by macrophages, multinucleated giant cells, fibroblasts, and collagen deposits, and it frequently cal-cifies. Within this granuloma the bacteria are kept at bay but remain viable. At some point in the future, perhaps due to a depression in the host’s resistance, the bacteria may grow again.

Question 37

How to Diagnose TB

Answer 37

Clinical symptoms
2 or more weeks of cough
Fever
Weight loss
Direct sputum smear and
microscopy
Chest x-ray
Mantoux skin test
Culture
Polymerase Chain Reaction