Mycobacteria

Question 1

What is unique about the cell walls of mycobacteria?

Answer 1

High lipid content, gram-positive but they repel analine dyes so they may appear beaded upon staining

Question 2

What kind of culture is used for mycobacterium leprae?

Answer 2

None, they are non-cultivable

Question 3

What, specifically, does the TST test look for?

Answer 3

A cell-mediated immune response to tuberculosis

Question 4

What conditions particularly predispose a person to developing active Tb disease?

Answer 4

Immunosuppression - aging, HIV infection, glucocorticoid use, etc

Question 5

From 1985 to 1992 the Tb rate in the US actually increased. Why?

Answer 5

Immigration from countries with high Tb rate, AIDS, injection drug use, curtailment of public health programs

Question 6

Where do Tb bacilli replicate?

Answer 6

In macrophages

Question 7

Ghon Focus

Answer 7

A Tb lesion, typically in the subpleural area of mid lung created by the granulomatous response

Question 8

Ghon complex

Answer 8

Peripheral ghon focus (a Tb lesion) with involved hilar lymph nodes

Question 9

Where in the lung do progressive primary and secondary (cavitary) tb infections occur respectively?

Answer 9

Progressive primary - mid lung, Secondary - apical posterior sections, upper lobes

Question 10

Miliary tuberculosis

Answer 10

Infection at multiple sites with characteristic small, yellowish lesion (resembles a millet seed)

Question 11

Besides the lung, where are common sites of miliary Tb infection?

Answer 11

Lymph nodes, kidney, adrenals, marrow, spleen, liver

Question 12

Why is secondary Tb infection also called Cavitary tb?

Answer 12

The immune response leads to tissue necrosis and cavitation

Question 13

Common symptoms of Tb infection

Answer 13

Low-grade fever, night sweats, weight loss, productive cough, hemoptysis (blood in sputum)

Question 14

Does erythema (redness) alone at TST test injection site indicate a positive test?

Answer 14

No, requires induration of a specific diameter

Question 15

What are some bacteria included in the mycobacterium tuberculosis complex?

Answer 15

Mycobacterium tuberculosis, Mycobacterium bovis (BCG vaccine), Mycobacterium ulcerans, and Mycobacterium Africanum

Question 16

Which bacteria in the mycobacterium Tb complex are included in the runyon classification and what are the groups of the runyon classification?

Answer 16

Includes all besides Mycobacterium Tuberculosis. Group 1 - Photochromogens, Group 2 - Scotochromogens, Group 3 - Nonphotochromogens, Group 4 - Rapid growers

Question 17

What Runyon group is Mycobacterium Kansasii in, what type of infection does it produce, where is it common, and what do you treat it with?

Answer 17

Is a Group I (Photochromogen), produces infection similar to Tb, seen in midwest, treat with anti-Tb drugs

Question 18

What will likely be in the history of someone infected with mycobacterium marinum?

Answer 18

Cut their hands in salt or fresh water, or have recently handled fish

Question 19

What runyon group is Mycobacterium Avium-Intracellulare-Complex in, who does it particularly infect, and what do you treat with?

Answer 19

Group II (Scotochromogens) and some in Group III, esp infects HIV-positive pts and those with lung disease, difficult to treat (not susceptible to anti-Tb drugs)

Question 20

What runyon group is mycobacterium haemophilum in, who in particular does it infect, what does it require?

Answer 20

Is in Group 3 (nonphotochromogens), infects immunosuppressed, requires iron ions to grow

Question 21

What type of infections do the Runyon Group 4 organisms cause and give 3 organisms in this group

Answer 21

Skin infections in immunocompromised pts. Mycobacterium fortuitum, Mycobacterium chelonae subsp chelonae, Mycobacterium chelonae subsp abscessus

Question 22

For what type of bacteria can you not use a swab specimen and why?

Answer 22

Mycobacteria, due to hydrophobicity they cling to swab material and dont get into culture

Question 23

Culture media for mycobacteria

Answer 23

Lowenstein-Jensen (LJ) and liquid media (albumen based)

Question 24

Difference between concentrated and direct smear specimens

Answer 24

Concentrated are digested, decontaminated (if necessary) and centrifuged. Direct are applied straight to slide

Question 25

When we use the term Acid Fast, in what sense is the word Fast used?

Answer 25

As in to hold fast. Acid fast positive specimens resist decolorization in presence of acid

Question 26

Are mycobacteria acid fast positive or acid fast negative?

Answer 26

Acid fast positive (resist decolorization in presence of acid)

Question 27

Two methods of amplification used for mycobacterium tuberculosis

Answer 27

PCR and Transcription-mediated amplification (TMA)

Question 28

In what cases is amplification used for mycobacterium tuberculosis infection?

Answer 28

Only with smear-positive specimens from pts with no prior history of Tb

Question 29

What two drugs are used in combination in Tb infections and why do we use both?

Answer 29

Isoniazid (INH) and Streptomycin. Use both because resistance to one is common

Question 30

What is the general pathology of leprosy (Hansens Disease)?

Answer 30

Chronic granulomatous disease of peripheral nerves and mucosa

Question 31

Who is more susceptible to leprosy, children or adults?

Answer 31

Children

Question 32

Which form of leprosy is more contagious

Answer 32

The lepromatous form is significantly more contagious than the tuberculoid form

Question 33

Differences between tuberculoid and lepromatous leprosy infections at the microscopic level

Answer 33

Tuberculoid - presence of many lymphocytes (among other cells), but few organisms in lesion, Lepromatous - few lymphocytes but many organisms in lesion

Question 34

Leonine facies

Answer 34

Diffuse symmetric thickening of loose skin on lips, forehead, and ears. Seen in lepromatous leprosy

Question 35

Which mycobacterial disease is diagnosed solely by staining and why?

Answer 35

Leprosy, because M. leprae doesnt grow in culture