Mycobacteria - Part 1

Mycobacteria include Mycobacterium tuberculosis (MTB) and other non-tuberculosis mycobacterium (NTM).
Around 100 recognized and proposed species under the genus Mycobacterium.
Strictly aerobic and intracellularly living organisms.
Non-spore forming except for Mycobacterium marinum which is spore forming.
Non motile, thin, slightly curved or straight rod-shaped organisms.
Extremely slow-growing: weeks necessary for noticeable growth (2-6 weeks for disease-related species).

Acid-fast Cell Wall
- Contains N-glycolyermic acid with a very high lipid content.
- Difficult to stain with traditional methods like Gram staining.
- Requires increased dye uptake time or the use of heat; resists decolorization with acid ethanol.
- This trait leads to the abbreviation AFB (Acid Fast Bacilli).

Causative agent of tuberculosis (TB).
Enhanced growth in 5-10% CO2 environments; complex media required (e.g., Lohenstein Jensen agar).
Historical context: first described by Robert Koch in 1882; a leading cause of morbidity and mortality.
Estimated 1/3 of the world's population infected; 1.5 million TB-related deaths in 2014.

Causative agent of Hansen disease (leprosy).
Unique inability to grow in vitro; can only be cultivated in armadillos and the footpads of mice.

Found in nature (soil and water); infections acquired via trauma, inhalation, or ingestion.
Opportunistic pathogens affecting patients with lung disease, immunosuppression, or percutaneous trauma.
Not transmissible person-to-person.

Group 1: Photochromogens
- Very slow-growing; colonies become pigmented upon light exposure.
- Example species: Mycobacterium cansassi, Mycobacterium marinum.
Group 2: Scotochromagens
- Slow-growing; pigmented when grown both in light and dark.
- Example species: Mycobacterium gordonae; rarely recovered.
Group 3: Nonphotochromogens
- Slow-growing; no pigment production regardless of growth conditions.
- Mostly pathogenic; includes Mycobacterium avium complex, Mycobacterium xenopi.
Group 4: Rapid Growers
- Grow within 7 days on routine media; cause infections primarily from post-traumatic wounds.
- Example species: Mycobacterium fortuitum, Mycobacterium chelonae.

Mode of transmission: inhalation of droplets from person-to-person.
Infection typically occurs in the alveoli of the lungs.
Once in the body, phagocytized by immune cells and multiplies within them.
Immunological response occurs 4-6 weeks post-infection, led by T cells; may form granulomas that can remain dormant.

Individuals with HIV are more susceptible to TB.
Reactivation risk factors include advanced age, immunosuppression (AIDS, drugs), malnutrition, alcoholism, and incarceration.

In children: nonproductive cough, potentially with shortness of breath.
In adults: can develop into progressive pulmonary TB.
Positive tuberculin skin test indicates prior exposure; uses purified protein derivatives of MTB.
Skin test outcomes:
- 5-9 mm: category 1 positive
- 10-14 mm: category 2 positive
- >15 mm: category 3 positive.

Primary Active Tuberculosis
- Can lead to disseminated TB via lymphatic spread.
- Common in patients with ineffective cellular immunity.
Latent Tuberculosis
- No apparent signs or symptoms; not infectious.
- Can reactivate under weakened immunity conditions.
Reactivation of Tuberculosis
- Occurs in situations where cellular immunity is compromised.
- Symptoms include fever, night sweats, chills, fatigue, and weight loss.

Slow-growing with a raised, dry, and rough appearance.
Lack pigmentation; may be buff-colored.
Presence of cord factor, leading to cell arrangements resembling long slender formations, crucial for virulence and survival in hosts.

Treatment failure potential due to:
- Inappropriate antimicrobial use
- Patient noncompliance
- Drug-resistant mycobacteria acquisition.
Resistance often arises from using single drugs; emphasizes the need for combination therapy.

A slow-growing species commonly found in the environment (soil, water, particularly coastal marshes).
Most common non-tuberculosis mycobacterium in the U.S.; primarily seen in immunocompromised patients.
Can also affect swine, cattle, and poultry.

Particularly affects middle-aged men with smoking history and pre-existing lung disease.
Increased isolation of Mycobacterium avium due to HIV/AIDS demographics.
Colonies: very slow-growing, thin with a non-pigmented transparent or opaque appearance.
Microscopic appearance: short, coccobacillary, uniformly stained without banding.

Surgical excision combined with chemotherapy for localized non-pulmonary disease.
Note: Mycobacterium avium complex shows partial resistance to TB drugs; necessitates higher drug concentrations and combination therapies.

Most are photochromogens; carotene pigment produced with light exposure.
Second most common cause of non-tuberculous lung disease in the U.S.
Causes chronic pulmonary lung disease, primarily affecting the upper lobes without scarring.
Colonies on Lohenstein Jensen agar: smooth to rough texture, wavy edges, and dark centers.
Microscopic observation: long rods with distinct cross banding.