Mycobacteria Flashcards
clinical diseases in the mycobacterium category
- tuberculosis
- leprosy
- non-tuberculous mycobacterial (NTM) infections
TB epidemiology
*about 25% of the world’s population has infection (most is latent)
*TB is one of the deadliest diseases in the world
M. tuberculosis complex
M. tuberculosis, M. africanum, M. bovis, M. miroti
mycobacterium tuberculosis - physiology
*acid-fast bacilli
*aerobic
*non-spore forming
*WAXY CELL ENVELOPE
mycobacterium tuberculosis - waxy cell envelope
*made of mycolic acids & lipids
*confers acid-fastness and impermeability to gram staining
*resistance to acid, alkali, drying, and germicides
*KILLED BY HEAT
*resistance to killing by antibody and complement
*slow growth
mycobacterium tuberculosis - virulence factors
*cord factor (TDM)
*sulfatides
mycobacterium tuberculosis - cord factor
-most abundant glycolipid in the mycobacterial CELL WALL
*toxic to mammalian cells
*inhibits neutrophils (PMNs)
*causes organism to cluster/arrange into “serpentine cords”
mycobacterium tuberculosis - sulfatides
*surface glycolipids
*INHIBIT fusion of phagosome and lysosome
*avoid exposure to lysosomal hydrolases (avoid host defenses)
mycobacterium tuberculosis - acid-fast stain
*use acid-fast stain for TB
*stain a RED color
*termed “red snappers”
mycobacterium tuberculosis - acid-fast culture
*culture is the gold standard for TB
*both solid and liquid media used
*slow growing (must incubate for a while)
mycobacterium tuberculosis - pathogenesis, ID50, and formation of ?
*acquired by INHALATION of aerosolized respiratory droplets
*LOW INFECTIOUS DOSE (ID50)
*pulmonary macrophages phagocytose the TB, but do not kill, so they proliferate
*T cells initiated
*macrophages and T cells wall of the infection, forming GRANULOMAS
mycobacterium tuberculosis - caseating granulomas
*caseation (middle of granuloma) = areas of necrosis, loss of tissue architecture
-caused by TNF, ROS, and cytotoxic agents
*granuloma = rim of healthy macrophages and T cells that are walling off; keeps TB from spreading throughout the body
mycobacterium tuberculosis - risk factors
*exposure / environmental factors
impaired immunity (esp HIV**)
mycobacterium tuberculosis - Ghon complex
- ghon focus/lesion - initial granuloma formed
- hilar lymphadenopathy
mycobacterium tuberculosis - latent TB
*immune system contains infection
*asymptomatic
*NOT contagious
*CAN advance to active TB
mycobacterium tuberculosis - active TB
*TB is active and grows in the body
*patients develop symptoms
*can spread from person to person (contagious)
*progressive disease can result in death
mycobacterium tuberculosis - s/s of active TB
*fever
*night sweats
*weight loss
*cough
*hemoptysis (coughing up blood)
mycobacterium tuberculosis - risk factors of progression to active TB
***HIV infection
**malnutrition
-intensity of exposure
-age
-alcohol use disorder
-diabetes
-homelessness/incarceration
-immunosuppression
mycobacterium tuberculosis - screening for latent TB
- tuberculin skin test
OR - interferon gamma release assay (IGRA)
mycobacterium tuberculosis - screening for active TB
- imaging (CXR or CT)
- sputum (AFB smear & culture; PCR)
- biopsy
mycobacterium tuberculosis - suspected active TB management (waiting for Dx)
*should be placed in special respiratory isolation (negative pressure room + N95 masks)
cavitary tuberculosis
*classic REACTIVATION disease (from latent to active)
*s/s: fever, night sweats, weight loss, productive cough
*CXR with cavities (esp apical)
*high communicability
*dx: AFB smears and cultures +
miliary tuberculosis
*disseminated form of T, spread through the BLOOD
*lung involvement + EXTRAPULMONARY sites
*characteristic “millet seeds” on CXR
common sites of extrapulmonary TB
-meningitis
-pleuritis
-pericarditis
-renal TB
-spine
-lymphadenitis (scrofula)
TB - management principles
*long-term Rx with a COMBINATION of drugs (for ACTIVE TB)
*2 phases (initial intensive + continuation phase)
leprosy (Hansen’s disease)
*acid-fast bacillus (M. leprae)
*primarily infects SKIN and PERIPHERAL NERVES (esp hands/feet)
leprosy - clinical disease
- lepromatous (multibacillary) - diffuse presentation, leonine facies; more severe
- tuberculoid (paucibacillary) - few hypoesthetic (NO SENSATION) skin plaques
non-tuberculous mycobacterium (NTM)
*acid-fast bacilli (M. marinum, M. avium complex, or M. scrofulacem)
*found in the ENVIRONMENT
non-tuberculous mycobacterium (NTM) - MAC/MAI
*can cause:
1. respiratory disease
2. disseminated disease
non-tuberculous mycobacterium (NTM) - M. scrofulacem
*causes cervical lymphadenitis
*more common in children
non-tuberculous mycobacterium (NTM) - M. marinum
*causes nodular skin lesion
*associated with water
