Mycobacteria Flashcards
Main pathogenic mycobacteria include?
M.tuberculosis
M.leprae
What do we refer to the non-tuberculous mycobacteria? (they cause opportunistic infections)
MOTTs (Mycobacterium Other Than Tuberculosis)
What are the general characteristics of mycobacteria? (Staining,morphology,motility,spores,capsule, aerobicity)
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
Important pathological properties include?
• 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
Describe the cell wall of mycobacteria.
Contains mycolic acid
Cord factor
Wax-D
What are the properties conferred by its high lipid content?
Impermeability to stains and dyes;acid-fastness
Slow growth
Antigenicity
Clumping
Resistance
What is mycobacteria resistant to?
many antibiotics
killing by acidic and alkaline compounds
osmotic lysis via complement deposition
lethal oxidations and allows survival inside of macrophages
List the virulence factors of TB.
Capsule- polysaccharide;prevents phagocytosis
Heat shock protein
Lipid cell wall
which special medium is required for its growth? (state its components)
Lowenstein-Jensen medium
Coagulated whole egg
Glycerol
Potato flour
Mineral salts (magnesium sulfate, sodium citrate, potassium phosphate)
Malachite green-inhibits growth of pther bacteria
What contributes to its virulence? (different from virulence factors)
Intracellular growth
Detoxification of oxygen radicals
Slow generation time (15-20 hrs)
High lipid content in cell wall
Cord factor (trehalose 6, 6’ dimycolatę)
What does cord factor do?
Helps with immune evasion
Granuloma formation
Cytokine release
Explain modes of transmission (for M.tuberculosis and M.bovis)
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)
Explain pathogenesis of M.tuberculosis.
Pathogenesis of Tuberculosis (TB):
- Inhalation & Initial Infection: M. tuberculosis enters the lungs via aerosolized droplets and infects alveolar macrophages.
- Immune Response: Macrophages and immune cells (dendritic cells, lymphocytes) attempt to control the infection but may fail.
- Granuloma Formation: Bacteria survive inside macrophages, leading to granuloma development to contain the infection.
- Latent or Active Disease: Granulomas may remain controlled (latent TB) or break down due to immune suppression, leading to active TB.
- Dissemination: In severe cases, bacteria spread through the bloodstream to other organs (miliary TB).
Can M.tuberculosis establish latency? (Yes/No)
Yes
State 2 extrapulmonary manifestations of TB.
Miliry TB
Meningitis
State the three main symptoms of TB.
Fever
Night sweats
Weight loss
Specimen samples?
sputum
pleural fluid
What stain do we used for acid-fast?
Ziehl-Neelsen stain
Fluorescence staining
Whats the gold standard in TB diagnosis?
Culture.
Solid culture- Lowenstein Jensen
wait 6-8 weeks
Describe appearance of culture in M.tuberculosis.
Rough, thick, wrinkled, have an irregular margin, and are faintly buff colored.
Biochemical tests?
Nitrate reductase test positive
Niacin test positive
Catalase at 68°C - negative
Two first line antibiotics?
Rifampcin
Streptomycin
Prevention techniques include?
BCG vaccine.
Isolation of the infected.
Good ventilation.
What is the main disease caused by M.leprae
Hansen’s disease
Basic characteristics of M.leprae?
Obligate intracellular organism
Reservoir — infected humans; Low infectivity
Transmission: Skin-to-skin contact
In three short points,describe pathogenesis of M.leprae.
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
Two major manifesations of Hansen’s disease.
Leprosy
Peripheral neuropathy
State four differences between tuberculoid leprosy and lepromatous leprosy.
- Bacteria Amount
Tuberculoid: Few bacteria (strong immune response)
Lepromatous: Many bacteria (weak immune response) - Skin Lesions
Tuberculoid: Few, well-defined, hypopigmented patches
Lepromatous: Many, widespread nodules - Nerve Damage
Tuberculoid: Localized nerve damage → loss of sensation
Lepromatous: Severe nerve damage → loss of digits - Lepromin Test
Tuberculoid: Positive
Lepromatous: Negative
Tuberculoid-mild and localized
Lepromatous-severe and widespread
State one antibiotic against M.leprae.
Rifampicin
State the main manifestation of the following MOTTs:
M.avium-intracellulare complex
M.fortuitum-chelonei complex
M.marinum
M.ulcerans
M.avium-intracellulare complex- Pulmonary disease patterns
M.fortuitum-chelonei complex- ??
M.marinum- Fish tank granuloma
M.ulcerans- Buruli ulcer
