Mycobacterium Tuberculosis and Nontuberculosis Mycobacteria Notes

Mycobacteria are slender, slightly curved, or straight rods.
They have an extremely high lipid content due to the presence of mycolic acid (hydroxymetoxy acid).
They are acid-fast, meaning they retain dye even after acid washing, and are stained by basic fluid dyes.
They are slow-growing organisms, typically taking 2 to 6 weeks to grow at the optimum temperature.
Growth can sometimes be observed in 24-72 hours, but significant growth for classification usually requires 2-6 weeks.

NTMs, or nontuberculous mycobacteria are differentiated based on their growth rate and pigment production.

Greater than 1 billion people are infected with Mycobacterium tuberculosis (MTB).
MTB is especially prevalent in third-world countries like the Philippines.
15-20% of infected individuals develop the active disease.

Pulmonary tuberculosis can be contracted by inhaling droplets from a cough or sneeze of an infected person.
Transmission occurs through aerosols or close contact.
Infected individuals develop granulomas and scarring.

Inhalation of Mycobacterium tuberculosis leads to direct access to the lungs.
Cavities can open into the bronchi, spreading the mycobacteria through coughing.
During granuloma formation:
- Macrophages ingest TB.
- TB replicates, and cell lysis occurs.
- Activated macrophages and T cells are recruited, walling off the TB and cell debris, forming a granuloma.

In cases of immunosuppression (e.g., HIV, smokers, autoimmune diseases), reactivation of TB is possible.
5-10% of infected individuals progress to cavitary TB.
Tubercles (granulomas) form granulomatous lesions.
Cessation (caseation) occurs, forming cheese-like masses from the breakdown of tubercles.

MTB can infect the kidney, gut, lymph nodes, CNS (causing meningitis), joints (arthritis).
Pot's disease: MTB infecting the spine.
MTB can infect various organs.

Growth on media:
- Löwenstein-Jensen (LJ) medium: growth in approximately 3 weeks.
- Middlebrook 7H10 and 7H11: growth in approximately 5 days.
Colony appearance: often described as having a cauliflower-like appearance.

Acquired through ingestion of milk from infected cattle.
BCG (Bacillus Calmette-Guérin) is related to M. bovis and is used for immunization but can cause issues in immunocompromised individuals.
Colonial appearance: small, granular, rounded white colonies with irregular margins, resembling water droplets in Middlebrook medium.

Mycobacterium asiaticum: Causes rare pulmonary infections.
Mycobacterium kansasii: Also known as yellow bacillus; second most common NTM in lungs; causes chronic pulmonary and extrapulmonary disease.
Mycobacterium simiae: Rare pulmonary infection, acquired through contamination.

Mycobacterium gordonae: Also known as tap water bacillus; rarely implicated in disease.
Mycobacterium szulgai: Causes pulmonary infection; photochromogenic at 22°C and scotochromogenic at 37°C.
Mycobacterium scrofulaceum: Causes cervical lymphadenitis in children.
Mycobacterium xenopi: Pulmonary and extrapulmonary infection; grows best at 42°C; forms bird's nest colonies in cornmeal agar.

White or tan-colored colonies.
Mycobacterium avium complex (MAC): most commonly isolated NTM, especially in immunocompromised patients such as AIDS patients; includes Mycobacterium avium subspecies paratuberculosis, example, Lyme disease and Crohn's disease frosting. also associated with AIDS patients, causing systemic disease.
Mycobacterium haemophilium: Requires hemoglobin and hemin to multiply.
Mycobacterium ulcerans complex: Causes Buruli ulcers; third most common mycobacteria.

Mycobacterium abscessus group: localized cutaneous infection; nonphotochromogen.
Mycobacterium chelonae: disseminated infections in immunocompromised patients; considered nonphotochromogens.
Mycobacterium fortuitum: cause of nosocomial infections; photochromogen.

Mycobacterium leprae: causative agent of leprosy (Hansen's disease).
- Tuberculoid leprosy: stimulation and peripheral nerve involvement.
- Lepromatous leprosy: severe, with extensive skin lesions and symmetric nerve damage, causing tissue death.

Specimen Collection: Collected in sterile, leak-proof containers.
Biosafety Levels:
- Biosafety level 2 (BSL-2) laboratory for culture.
- Biosafety level 3 (BSL-3) practices for propagation or culture, performed in Class II or Class III biosafety cabinets.

Specimens include sputum, other secretions, gastric aspirate/washings, urine, stool, blood, tissue, and body fluids.
Sputum: Early morning, three consecutive days; collected via:
- Transthoracic aspiration
- Bronchoscopy swabbing (using a Stevoid tube for aspirates)
Gastric aspirate and washings: Lavage; three specimens collected within three days using a 11F tube; 20-25 ml in a 50 ml conical tube for gastric fasting.
Urine: Three consecutive days, midstream collection - first few ml of urine after voiding are discarded.
Blood: Isolation for disseminated Mycobacterium avium complex (MAC), particularly in AIDS patients; recovered by radiometric Bactec 13A vial or by isolator lysis centrifugation system.
Tissue and body fluids: E.g., CSF for tuberculosis meningitis, pleural, pericardial (heart), and peritoneal (abdomen) fluids.

Not accurate or sensitive; determines if there has been exposure to TB or Mycobacterium tuberculosis.
Cross-reactions from other types of mycobacteria.
Suggest obsolete approach for educational purposes because not as reliable as other blood tests.