Mycobacterial Infections

Question 1

Mycobacteria

Answer 1

• high lipid contend (must stain with acid fast even though G+)
• slow growing, so disease are chronic and slowly progressive

Question 2

Tuberculosis

Answer 2

• M. tuberculosis (hominis or bovis)
• obligate aerobe, bacillus
• chronic, communicable disease
• causes spherical granuloma with central caseous necrosis
• transmitted via aerosolized droplets
• Primary and Secondary illnesses
• proliferate within macrophages
• cell mediated immunity causes caseous granulomas

Question 3

Progressive Primary TB

Answer 3

• host immune response fails to control bacilli

- Ghon focus enlarges, can invade bronchial tree or cause distal lung collapse

Question 4

Miliary TB

Answer 4

• infection disseminates and causes small yellow lesions in several organs
• may progress to meninges

Question 5

Secondary (Cavitary) TB

Answer 5

• happens in someone who has previously had infection
• lungs are most common site
• T cell mediated immune response to TB antigens lead to tissue necrosis and cavitation

Question 6

Leprosy

Answer 6

• M. leprae, Acid fast rod
• destructive process involving peripheral nerves, skin, and mucous membranes
• multiplies best at temperatures below core

Question 7

Tuberculoid leprosy

Answer 7

• hyperergic individuals with strong immune response
• characterized by single lesion usually on face, extremities, or trunk
• granulomas resemble those of TB but lack caseation
• minimal disfigurement, not contagious

Question 8

Lepromatous leprosy

Answer 8

• multiple timor like lesion of skin, eyes, testes, nerves, lymph nodes, spleen
• macrophages act as microincubators for bacteria
• skin lesions may ulcerate

Question 9

Mycobacterium avium-intracellulare

Answer 9

• MAI complex
• third most common opportunistic infection in AIDS patients in US
• in immunocompromised: resembles TB but progresses slower, usually in elderly with preexisting lung process
• in AIDS patients: lack helper T cells that normally prevent MAI infection, macrophages can’t kill organism, spread throughout lymph and blood, cause expanding nodular lesions

Question 10

Atypical Mycobacteria

Answer 10

• M. kansasii - granulomatous pulmonary disease
• M. scrofulacerum - cervical lymphadenitis in young children
• M. marinum - swimming pool granuloma
• M. ulcerans - severe ulcerating skin disease
• M. chelonae/fortuitum - traumatic inoculations