Ch. 28 - Mycobacterium

Question 1

Mycobacterium

Answer 1

Aerobic, acid-fast bacilli (mycolic acids don’t decolorize)
Non-motile
Non-spore forming

Cell walls rich in lipids --> mycolic acids
Mycolic acids provide: 
- acid-fastness 
- slow growth
- detergent, antibiotic resistance
- antigenicity
- clumping

Question 2

Runyon Classification

Answer 2

For NTM (nontuberculosis Mycobacterium)

Slow-growing photochromogens (pigment in exposure to light)

Slow-growing scotochromogens (pigment in absence of light)

Slow-growing non-pigmented

Rapidly growing

M. Tuberculosis complex - slow-growing non-pigmented or light tan color

Question 3

Mycobacterium tuberculosis (M. Tb)

Answer 3

Aerobic, acid-fast bacilli

Intracellular (inhibit phagolysosome fusion)

Via resp. tract (inhalation)

Many bacteria –> tissue necrosis
No toxin/enzyme

Granuloma formation (small - killed; large, necrotic - encapsulated in fibrin)

Bacteria can remain dormant

Humans only known reservoir

Question 4

M. Tb disease/diagnosis

Answer 4

Most infections in middle to lower lungs, can be anywhere

Diagnosis with x-ray and positive PPD skin test

Question 5

Mycobacterium leprae

Answer 5

Aerobic, acid-fast bacilli

Cause leprosy (Hansen disease) (person-person spread)

Tuberculoid leprosy - ^ cellular response; few bacteria

Lepromatous leprosy - ^ Ab response; many bacteria
Most infectious form
Deforming skin lesions

Lepromin skin test

Question 6

Mycobacterium avium/MAC

Answer 6

MAC - Mycobacterium avium complex

disease in immunocompromised

pulmonary disease seen in immune-competent pts.

tons of bacteria

ingestion of bacteria, not person-person, contaminated aerosols

replication in localized lymph nodes, then systemic spread