Mycobacteria

Question 1

Main pathogenic mycobacteria include?

Answer 1

M.tuberculosis
M.leprae

Question 2

What do we refer to the non-tuberculous mycobacteria? (they cause opportunistic infections)

Answer 2

MOTTs (Mycobacterium Other Than Tuberculosis)

Question 3

What are the general characteristics of mycobacteria? (Staining,morphology,motility,spores,capsule, aerobicity)

Answer 3

Acid fast slim, rod-like
• Gram positive-like cell wall structure
• Cell wall has peptidoglycan but 60% is lipids
• Resists decolorization by acid- alcohol -> acid-fast staining

Non-motile
Non-sporing
capsulated
Strict aerobes

Question 4

Important pathological properties include?

Answer 4

• Do not produce exotoxins or endotoxins
• Disease processes largely a result of delayed-type hypersensitivity reaction to mycobacterial proteins
• Elicit a granulomatous response
• Chronic course of disease

Human strains show heavy growth on culture (eugonic) than bovine strains which have poor growth (dysgonic) on glycerol- containing media

Question 5

Describe the cell wall of mycobacteria.

Answer 5

Contains mycolic acid
Cord factor
Wax-D

Question 6

What are the properties conferred by its high lipid content?

Answer 6

Impermeability to stains and dyes;acid-fastness
Slow growth
Antigenicity
Clumping
Resistance

Question 7

What is mycobacteria resistant to?

Answer 7

many antibiotics
killing by acidic and alkaline compounds
osmotic lysis via complement deposition
lethal oxidations and allows survival inside of macrophages

Question 8

List the virulence factors of TB.

Answer 8

Capsule- polysaccharide;prevents phagocytosis
Heat shock protein
Lipid cell wall

Question 9

which special medium is required for its growth? (state its components)

Answer 9

Lowenstein-Jensen medium

Coagulated whole egg
Glycerol
Potato flour
Mineral salts (magnesium sulfate, sodium citrate, potassium phosphate)
Malachite green-inhibits growth of pther bacteria

Question 10

What contributes to its virulence? (different from virulence factors)

Answer 10

Intracellular growth
Detoxification of oxygen radicals
Slow generation time (15-20 hrs)
High lipid content in cell wall
Cord factor (trehalose 6, 6’ dimycolatę)

Question 11

What does cord factor do?

Answer 11

Helps with immune evasion
Granuloma formation
Cytokine release

Question 12

Explain modes of transmission (for M.tuberculosis and M.bovis)

Answer 12

Modesof transmission
• Droplet infection Person to person by inhalation aerosols
• M.tuberculosis (Pulmonary tuberculosis)

• Ingestion of milk
• Infected cattle
• M.bovis (Intestinal tuberculosis)

• Contamination of abrasion
• Laboratory workers (Skin infection)

Question 13

Explain pathogenesis of M.tuberculosis.

Answer 13

Pathogenesis of Tuberculosis (TB):

1. Inhalation & Initial Infection: M. tuberculosis enters the lungs via aerosolized droplets and infects alveolar macrophages.
2. Immune Response: Macrophages and immune cells (dendritic cells, lymphocytes) attempt to control the infection but may fail.
3. Granuloma Formation: Bacteria survive inside macrophages, leading to granuloma development to contain the infection.
4. Latent or Active Disease: Granulomas may remain controlled (latent TB) or break down due to immune suppression, leading to active TB.
5. Dissemination: In severe cases, bacteria spread through the bloodstream to other organs (miliary TB).

Question 14

Can M.tuberculosis establish latency? (Yes/No)

Answer 14

Yes

Question 15

State 2 extrapulmonary manifestations of TB.

Answer 15

Miliry TB
Meningitis

Question 16

State the three main symptoms of TB.

Answer 16

Fever
Night sweats
Weight loss

Question 17

Specimen samples?

Answer 17

sputum
pleural fluid

Question 18

What stain do we used for acid-fast?

Answer 18

Ziehl-Neelsen stain
Fluorescence staining

Question 19

Whats the gold standard in TB diagnosis?

Answer 19

Culture.
Solid culture- Lowenstein Jensen
wait 6-8 weeks

Question 20

Describe appearance of culture in M.tuberculosis.

Answer 20

Rough, thick, wrinkled, have an irregular margin, and are faintly buff colored.

Question 21

Biochemical tests?

Answer 21

Nitrate reductase test positive
Niacin test positive
Catalase at 68°C - negative

Question 22

Two first line antibiotics?

Answer 22

Rifampcin
Streptomycin

Question 23

Prevention techniques include?

Answer 23

BCG vaccine.
Isolation of the infected.
Good ventilation.

Question 24

What is the main disease caused by M.leprae

Answer 24

Hansen’s disease

Question 25

Basic characteristics of M.leprae?

Answer 25

Obligate intracellular organism Reservoir — infected humans; Low infectivity Transmission: Skin-to-skin contact

Question 26

In three short points,describe pathogenesis of M.leprae.

Answer 26

Chronic lepromatous disease Main target cell of the bacilli is the Schwann cell with the resulting nerve damage causing anesthesia and muscle paralysis The first sign of leprosy is a non-specific or indeterminate skin lesion

Question 27

Two major manifesations of Hansen's disease.

Answer 27

Leprosy Peripheral neuropathy

Question 28

State four differences between tuberculoid leprosy and lepromatous leprosy.

Answer 28

1. Bacteria Amount Tuberculoid: Few bacteria (strong immune response) Lepromatous: Many bacteria (weak immune response) 2. Skin Lesions Tuberculoid: Few, well-defined, hypopigmented patches Lepromatous: Many, widespread nodules 3. Nerve Damage Tuberculoid: Localized nerve damage → loss of sensation Lepromatous: Severe nerve damage → loss of digits 4. Lepromin Test Tuberculoid: Positive Lepromatous: Negative Tuberculoid-mild and localized Lepromatous-severe and widespread

Question 29

State one antibiotic against M.leprae.

Answer 29

Rifampicin

Question 30

State the main manifestation of the following MOTTs: M.avium-intracellulare complex M.fortuitum-chelonei complex M.marinum M.ulcerans

Answer 30

M.avium-intracellulare complex- Pulmonary disease patterns M.fortuitum-chelonei complex- ?? M.marinum- Fish tank granuloma M.ulcerans- Buruli ulcer