B4.4 MYCOBACTERIUM TUBERCULOSIS COMPLEX Flashcards
What is the size range of Mycobacteria?
0.2 to 0.6 µm x 1 to 10 µm
Are Mycobacteria motile, spore-forming, or encapsulated?
No, Mycobacteria are nonmotile, non-spore-forming, and non-encapsulated.
What feature of the Mycobacterial cell wall contributes to acid fastness?
The presence of N-glycolylmuramic acid and a high lipid content.
What type of respiration do Mycobacteria exhibit, and what enzyme activity are they known for?
Mycobacteria are strictly aerobic and catalase positive.
What appearance is often observed in Mycobacteria due to Much’s granules?
A beaded appearance, with Much’s granules being non-acid-fast and gram-positive.
What structural formations can Mycobacteria exhibit microscopically?
Palisade or snapping formations, including X, Y, V, and L forms.
How quickly do rapidly growing Mycobacteria grow, and at what temperature range?
They grow on simple media in 2 to 3 days at 20°C to 40°C.
How long do Mycobacteria associated with disease take to grow, and on what type of media?
They require 2 to 6 weeks of incubation on complex media.
What is the optimal pH range for Mycobacterial culture media?
6.5 to 6.8
What is the generation time for Mycobacteria?
Greater than 12 hours
What type of medium is required for the primary isolation of Mycobacterium tuberculosis (MTB)?
A complex medium containing egg-potato base or serum-agar base
What environmental conditions are needed for MTB growth?
Very slow growth (10–20 days for visible colonies).
Requires increased CO₂ tension (5–10%) at 37°C.
Describe the appearance of MTB colonies.
Initially: Small (1–2 mm), dry, friable, rough, warty, granular, and buff-colored.
Later: Flat irregular margins with a “cauliflower-like” center.
What enhances MTB growth, and how is this described?
Glycerol enhances growth, described as eugenic growth (luxuriant growth).
What is the replication time of MTB?
20–22 hours
What factors enable MTB to resist adverse environmental conditions?
Intracellular existence in the body.
Resistance to drying, heat, and chemical agents
What are the main virulence factors of MTB,
Cord Factor (Trehalose-6,6’-dimycolate)
Sulfatides
Responsible for tight serpentine cords and cord formation.
Cord Factor (Trehalose-6,6’-dimycolate)
Glycolipids that react with neutral red and are associated with virulent MTB strains.
Sulfatides
What is the primary disease caused by MTB, and how is it transmitted?
Primary Tuberculosis: Chronic granulomatous infection of the respiratory tract.
Transmission: Inhalation of infected droplets (1–5 µm).
What are the key symptoms of primary tuberculosis?
Cough,
hemoptysis,
chest pain,
dyspnea,
low-grade fever,
night sweats,
fatigue,
anorexia, and
weight loss.
Hypersensitivity to MTB proteins, indicating past or recent TB infection.
Tuberculin Test
What reagents are used in tuberculin testing?
Old Tuberculin (OT): Prepared from boiled broth cultures.
Purified Protein Derivative (PPD): Mixture of small tuberculoproteins
What methods are used for tuberculin test administration?
Mantoux Test (intracutaneous injection).
Von Pirquet Test (skin scratching).
Vollmer Patch Test (cloth soaked in OT/PPD placed on skin).
Moro Percutaneous Test (OT/PPD + lanolin rubbed onto skin).
Tuberculin Tine Test (multiple punctures)
How is the tuberculin test interpreted?
Read at 48–72 hours.
Measure induration:
≥10 mm = Positive.
5–10 mm = Doubtful (other mycobacteria).
<5 mm or erythema without induration = Negative
Hematogenous spread of MTB, seeding multiple organs (spleen, liver, lungs, bone marrow, kidneys, etc.).
Miliary TB
MTB invades the spinal vertebrae, causing back pain
Pott disease
Pott disease Also known as
skeletal TB or tuberculosis spondylitis
Name other forms of extrapulmonary TB.
Pleural TB (pleurisy).
Lymphadenitis (painless head or neck swellings).
Meningeal TB (rupture into subarachnoid space).
Genitourinary infections (kidneys/genital organs).
Peritoneal TB.
Gastrointestinal TB.
What are the first-line antituberculosis drugs?
Rifampin,
Isoniazid (INH),
Pyrazinamide (PZA), and
Streptomycin
What defines Multidrug-Resistant TB (MDR-TB)?
Resistance to at least isoniazid and rifampin
What defines Extensively Drug-Resistant TB (XDR-TB)?
Resistance to:
Isoniazid and rifampin.
Any fluoroquinolone.
At least one injectable second-line drug (e.g., amikacin, kanamycin, or capreomycin).
Biochemical Tests for MTB
Niacin Accumulation: Positive.
Nitrate Reduction: Positive.
Catalase: Positive.
Heat-stable Catalase (68°C): Negative.
Arylsulfatase: Negative.
Pyrazinamidase: Positive.
Inhibited by NAP: Positive.
Resistance to T2H: Positive.
What is the primary host for Mycobacterium bovis
Primarily cattle, but also dogs, cats, swine, parrots, and humans
What is the transmission route for Mycobacterium bovis
Ingestion of contaminated milk or exposure to infected animals
What vaccine is derived from M. bovis?
Bacillus-Calmette-Guerin (BCG),
used for newborn vaccination against TB.
Bacillus-Calmette-Guerin (BCG)
Describe the cultural characteristics of M. bovis colonies on Egg-based media
Slow-growing, small, granular, rounded, nonpigmented colonies with irregular margins after 21 days at 37°C.
Describe the cultural characteristics of M. bovis colonies on Middlebrook 7H10 medium
Similar colonies to MTB but slower to mature
What medium component selectively inhibits M. bovis growth
Glycerol
Biochemical characteristics of M. bovis?
Niacin accumulation: Negative.
Nitrate reduction: Negative.
Heat-stable catalase: Negative.
T2H (Thiophene-2-carboxylic acid hydrazide): Sensitive.
Serpentine cords: Present in smears
Where is Mycobacterium africanum associated with human TB cases?
Tropical Africa.
What specialized test is used for M. africanum detection?
Spoligotyping (spacer oligotyping).
What are the biochemical characteristics of M. africanum?
Urease: Positive.
Variable growth in TCH (Thiophene-2-carboxylic acid hydrazide).
Smooth strain of MTB, grows more rapidly (6 days on solid media).
Mycobacterium canetti
From which patient population was M. canetti first isolated?
An AIDS patient with mesenteric TB
Biochemical characteristics of M. canetti?
Niacin: Positive.
Nitrate reduction: Positive
Which patient populations are affected by Mycobacterium microti?
Both immunocompetent and immunocompromised individuals.
Isolated from TB patients, indicating its clinical relevance in human infections.
M. microti
