T3: Mycobacterium (PART 1)

Question 1

What are the key identification tests for photochromogens?

Answer 1

• • Probe

- Heat resistant catalase

Question 2

What is the role of interferon gamma in granuloma formation in the Quantiferon Gold test (alternative test to TB skin tests)

Answer 2

Once lymphs are isolated and exposed to antibody, if they make gamma interferon it means they have M. tb (more expensive but also more sensitive/specific)

Question 3

Acid-fast organisms

Answer 3

*

Question 4

modified acid -fast organisms

Answer 4

*

Question 5

Define “rapid grower”

Answer 5

*Grow on solid media in less than a week

Question 6

Define “slow grower”

Answer 6

M. tb is an example. Takes 6-8 weeks to grow on plates

Question 7

What is the most reliable biochemical test for ID of M. tuberculosis?

Answer 7

*Niacin, TB test too? Cultures confirm diagnosis

Question 8

What is the most reliable biochemical test for ID of Mycobacteria?

Answer 8

About 70% ID’d with probes

Question 9

advantages of carbofuchsin acid fast stains

Answer 9

Fuschsin and phenol:

- stains all mycobacteria

Question 10

disadvantage of carbofuchsin acid fast stains

Answer 10

Fuschsin and phenol”

- less sensitive

Question 11

Advantages of fluorescent (Fluorochrome) acid fast stain

Answer 11

Auromine or Auromine-Rhoadmine:

- very sensitive

Question 12

disadvantage of fluorescent acid fast stains

Answer 12

Auromine or Auromine-Rhoadmine:

- poor for rapid growers

Question 13

Biochemical reactions of M. tuberculosis

Answer 13

Niacin (+)

T2H resistant

Question 14

M tuberculosis

- plate morphology

Answer 14

rough and buff

Question 15

What is the significance of cording in M. tuberculosis?

Answer 15

Cord factor makes the isolate more virulent

Question 16

Define and list examples:

Scotochromogen

Answer 16

Pigment in light or dark

- M. gordonae, M. flavescens, M. xenopi, M. szulgai, M. scrofulaceum

Question 17

Define and list examples:

- photochromogen

Answer 17

Pigment after light

- Ex: M. kansasii, M. marinum, M. simiae

Question 18

Define and list examples:

- nonchromogen

Answer 18

No yellow pigment

- M. tuberculosis, M. avium (will turn slt yellow after prolonged incubation

Question 19

Define and list examples:

- rapid grower

Answer 19

*Grow on solid media in less than a week

Ex: M. fortuitum, M. chelonei, M. absecessus

Question 20

Why can acid-fast bacteria stain acid-fast?

Answer 20

They have a high lipid content in cell well; resist decolorization with acid/ alcohol

Question 21

Why does the DNA probe used to ID M. tuberculosis targets ribosomal RNA and not chromosomal DNA?

Answer 21

this makes the assay more sensitive since there are 10,000 copies of RNA per bacterium and only 1-2 copies of DNA

Question 22

Type of lung involvement observed in primary vs secondary (reactivation) tuberculosis

Answer 22

Primary: mild-lung areas

Secondary TB reactivation TB: apical/upper lobes; more necrosis

Question 23

Overall incidence of TB in the U.S. population in:

African Americans, Caucasians, Hispanics and Asian heritage

Answer 23

80% in Blacks, Hispanics, and Asians 
20% in Whites
- Blacks: 25%
- Whites: 16%
- Hispanic: 29%
- Asian: 28%

Question 24

How do birth rates in the U.S. affect the distribution of TB ?

Answer 24

U.S. Born: Blacks >Whites > Hispanics > Asian

Foreign- Born: Asians >Hispanics >Blacks >Whites

Question 25

What countries/ continents in the world have the highest B mortality

Answer 25

South and South East Asia

Question 26

5 populations in the U.S. that are at increased risk for TB infections

Answer 26

• prisoners, nursing home, homeless shelters
• those living with TB patient
• Aids patients
• Illicit drug users
• Immigrants (last 5 years)