mycobacterial infections

Question 0

TB (acid-fast, obligate aerobes, takes 3-8wks to grow in culture), general

Answer 0

• caused by mycobacterium tuberculosis hominis (major), M. bovis (minor, unpasteurized milk from infected cows)
• COMMUNICABLE, CHRONIC DZ that only affects humans (risk: HIV+, malnourished, immigrants from endemic areas, elderly - reactivation) and spread by AEROSOLIZED RESP DROPLETS that targets LUNGS (major, other organs possible)

Question 1

4 mycobacterial infections (2 have no environmental reservoir (N), 2 are environmental organisms (E))

Answer 1

1. TB (N)
2. leprosy (N)
3. mycobacterium avium-intercellulare complex (E)
4. atypica mycobacteria (E)

Question 2

TB (primary)

Answer 2

• Primary: Asx usually. if host is immunocompetent –> granulomatous reaction. if organism burden is large –> hypersensitive –> fibrosis and necrosis (CASEOUS). if IC/immunologically immature: poorly formed granuloma and not contained –> progressive primary TB
• if active infection (constitutional sx, and hemoptysis) = organism growing in a person, independent of Sx;;;active infection is destructive, symptomatic dz.
• Primary TB: GHON FOCUS (small area of consolidation) + mediastinal/hilar LN involvement = GHON complex.
• primary TB leads to 1. (most) indolent self-limited -can lead to –> 2ary TB = CAVITARY TB (always an active dz), (reactivation of primary infection, also by exposure to exogenous organisms, IC)…2ary TB can lead to MILIARY TB via blood/lymphatics
  2. 10% aggressive = aka progressive primary TB (IC, children leads to –> MILIARY TB = dissemination of TB characterized by SMALL NODULAR,YELLOW LESIONS IN MENINGITIS, VERTEBRAE, LN, LUNGS, LIVER, SPLEEN, ADRENALS, JOINTS, LONG BONES.

SX: COUGH, WEIGHT LOSS, CONSTITUTIONAL SX, ANOREXIA, HEMOPTYSIS (risk of exanguination). UNTX 2ary infections eventually FATAL.

Question 3

leprosy (weakly acid fast, cant be cultured) - mostly from immigrants from endemic areas (tropicals)

AKA HANSEN DZ

Answer 3

• Mycobacterium leprae - loves low temps therefore mostly reside in NASAL secretions/ulcerated lesions that gets in via INOCULATIONs into resp tract/wound. causes CHRONIC, SLOW PROGRESSIVE DESTRUCTIVE PROCESS that involves PERIPHERAL NERVES, SKIN, MUCOUS MEMBRANES
  1. lepromatous leprosy: disfiguring (clear zones (epidermis separates from dermis (dermis is filled with macrophages filled with lepra bacilli)
  2. tuberculoid leprosy: self healing macules if host has immunity (hypersenstivity)

Question 4

mycobacterium avium-intracellulare complex (MAI) - THIRD most common OI in AIDS pts in the US

Answer 4

INHALED from soil, water, food.
1. rare, slowly progressive granulomatous PUL dz in immunocompetent (50-70yo) that resembles TB but much slow progression: PUL NODULES, CAVITIES, CASEATING GRANULOMAS.
-RISKS: copd, treated TB, pnuemoconiosis, bronchiectasis,
SX: COUGH ONLY, NOOOOO fever weight loss night sweats (thats often in TB)
-TX disappointing.
2. progressive systemic dz in pts with AIDS: bc dec Tcells (cannot activate macrophages therefore spreads).
SX: resembles TB at 1st. but with involvement of GUT (DIARRHEA), ABD APIN
TX: may control spread, rarely cure

Question 5

atypical mycobacteria

Answer 5

H2O, dirt, dust
INGESTING, INHALING, INCULATING
everything EXCEPT M. tuberculosis is ATYPICAL:
1. m. kansasii: similar to MAI in immunocompetent (>50yr)
2. m. scrofulaceum: SOIL (kids1-5yr): draining, granulomatous, cervical lymphadenitis (submandibular, if take out it is curative)
3. m. marinum: underwater surfaces, aka “swimming pool granuloma”. localized nodular skin lesion from traumatic abrasions (pyogenic or granulomatous)
4. m. ulcerans: severe ulcerating skin dz: Australia, Af. causes coagulative necrosis
5. m. fortuitum and m. chelonae: ubiquitous in environments. traumatic/iatrogenic inoculation –> abscesses –> pyogenic or granulomatous. HEALS SPONTANEOUSLY