Mycobacterial Diseases I

Question 1

One of the reasons people came to Colorado to treat tuberculosis is that ________________.

Answer 1

M. tuberculosis is an obligate aerobe and the lower oxygen content in Colorado prevents growth

Question 2

All mycobacteria are _______________.

Answer 2

obligate aerobes

Question 3

Mycobacteria are said to have a __________ coat.

Answer 3

“waxy” (from mycolic acid)

Question 4

Where are mycolic acids in relation to the mycobacterial cell membrane?

Answer 4

They are attached to polysaccharides on the outside of the cell membrane.

Question 5

How many people are killed by TB each year?

Answer 5

1.8 million (more than any other bacteria)

Question 6

TB is the leading killer in people with _________.

Answer 6

HIV

Question 7

Tuberculosis in the U.S. has been decreasing since ________.

Answer 7

1993 (there was a peak this year due to HIV)

Question 8

How is TB transmitted?

Answer 8

Respiratory droplets quickly evaporate and become small enough to reach alveoli.

Question 9

What percent of people exposed to TB develop infections?

Answer 9

30%

Question 10

Of the people who develop TB infection, what percent go into latency?

Answer 10

95%

Question 11

What molecule prevents fusion of phagosomes with lysosomes?

Answer 11

ManLAM

Question 12

PIM (phosphatidylinositol mannoside) induces ____________.

Answer 12

fusion of nutrient-rich endosomes with TB-containing phagosomes

Question 13

One of the reasons TB induces granuloma formation is that _____________.

Answer 13

large, discrete lesions will cause the host to cough, thus spreading TB

Question 14

What fraction of the Earth’s population has latent TB?

Answer 14

1/3

Question 15

Why does M. tuberculosis cause cavitations?

Answer 15

The air allows the bacteria to grow.

Question 16

___________ confers resistance to isoniazid.

Answer 16

katG (the catalase that activates the prodrug)

Question 17

Importantly, Mycobacteria cannot acquire _____________.

Answer 17

genes by transformation –only through point mutations

Question 18

Multiple studies have shown that ______________ is needed to eliminate TB.

Answer 18

a functioning immune system (that is, drugs alone cannot kill TB)

Question 19

______________ should always make you think of reactivated TB.

Answer 19

Upper lobe lesions

Question 20

Almost all facilities in the U.S. use _________ media because it is faster.

Answer 20

liquid

Question 21

One of the problems of treating TB worldwide is that ______________.

Answer 21

traditional diagnostics (which rely on cultures and biochemistry techniques) take months to give precise susceptibility data

Question 22

The strongest predictor of MDR TB is ____________.

Answer 22

past treatment for TB (with continuation or progression of symptoms)

Question 23

What are the cutoffs for TST induration?

Answer 23

• High risk: greater than 5 mm
• Intermediate risk: greater than 10 mm
• Low risk: greater than 15 mm

Question 24

Why does M. tuberculosis reactivate in the upper lobes?

Answer 24

Those are more aerated, and M. tuberculosis is an obligate aerobe.

Question 25

M. tuberculosis is highly durable because _______________.

Answer 25

of its mycolic acids that prevent desiccation and protect from disinfectants

Question 26

Cultures used to isolate M. tuberculosis are mixed with __________, which selectively kills most other bacteria.

Answer 26

alkali

Question 27

Although Mycobacteria are neither Gram-positive nor Gram-negative, they are more similar to _____________.

Answer 27

Gram-negative, because the mycolic acid layer has an outer membrane just like the peptidoglycan layer has an outer membrane in Gram-negative bacteria

Question 28

The initial TB infection is usually just ____________.

Answer 28

an influenza-like illness

Question 29

What is the primary immune response to M. tuberculosis?

Answer 29

Cell-mediated

Note: humoral immunity has no role in the elimination of or protection from tuberculosis.

Question 30

How does miliary TB develop?

Answer 30

In individuals with deficient macrophage response, the primary infection is not able to controlled and the bacilli are able to spread throughout the body.

Question 31

True or false: most of the symptoms of TB are the result of endotoxin.

Answer 31

False. The symptoms of TB are predominately from the immune response.

Question 32

How does the newer screening test for TB work?

Answer 32

You place patient blood in an incubator with proteins only found in M. tuberculosis (not in M. bovis –hence, it can differentiate between BCG and exposure) and measure the amount of IFN-gamma released overnight.

Question 33

Which mycobacterium is hardest to kill?

Answer 33

M. abscessurs

Question 34

Hypopigmented, anesthetic skin patches are characteristic of ________________.

Answer 34

M. leprae infection

Question 35

Describe high-risk and intermediate-risk for TB.

Answer 35

• High-risk:

• HIV
• Recent past infection
• Recent immigrants from endemic areas
• IV drug users
• Immunosuppression

•Intermediate-risk:

• Healthcare workers
• Known contact with infected person

Question 36

True or false: TB is never fully eliminated, even with robust treatment.

Answer 36

False. About 95% of cases are full cures.

Question 37

Who is a candidate for treatment of LTBI?

Answer 37

Those with positive IGRAs or TSTs who have normal chest x-rays

(Abnormal x-rays prompt evaluation for active TB.)

Question 38

Non-tubercular mycobacteria tend to prefer ____________ climates.

Answer 38

warmer (except M. leprae)

Question 39

What organism causes Buruli ulcers?

Answer 39

M. ulcerans

Question 40

M. leprae preferentially affects the ______________.

Answer 40

skin, eyes, and mucosa of the URT