Filamentous and Mycobacteria - SRS

Question 1

What are the members of the CMN group?

Answer 1

Corynebacteria

mycobacteria

nocardia

Question 2

What is the gram stain character of the members of the CMN group?

Answer 2

Nocardia and actinomyces are gram positive

corynebacteria are gram positive and often pleomorphic

mycobacteria are gram ? (+ d/t cell wall structure but - d/t DNA)

Question 3

Mycobacteria have a polymer complex that is comprised of…

1. peptidoglycan
2. arabinogalactan
3. ?

Answer 3

Mycolic acid

Question 4

Since mycobacteria and nocardia are “acid fast”, what stain is used for identification?

Answer 4

Ziehl-Neelsen stain

Question 5

Mycobacteria have something called cord factors, what are these and what do they do?

Answer 5

Dimycolates of trehalose that…

1. give rise to growth in serpentine rods
2. inactivate mitochondrial membranes of phagocytes, allowing organism to survive and multiply in phagocytes

Question 6

How is M. tuberculosis spread?

Answer 6

Airborne droplets

Question 7

How does M. bovis spread?

Answer 7

oropharyngeal and intestine via unpasteurized cow milk

Question 8

What are the two types of disease processes we see arise from M. leprae?

Answer 8

Tuberculoid leprosy

Lepromatous leprosy

Question 9

Tuberculosis has primary and secondary infection stages. Describe the primary infection stage.

Answer 9

1. Ghon complex
2. Granulomatous response, typically asymptomatic and self-limiting but clinically sympomatic in 5%

Question 10

What is the Ghon complex?

Answer 10

Parenchymal lesion and an involved lymph node

Question 11

Secondary Tb infection occurs when old walled off lesions are reactivated, usually in apical lung regions d/t high ppO₂. What is the course of the disease from this point?

Answer 11

Variabe, but often cavitary caseous necrosis with subsequent scarring or progressive disease

Question 12

What is shown in the attached picture? In what type of disease do we see this?

Answer 12

Scrofula - non-pulmonary TB may present with cervical lymphadenitis

Question 13

When does miliary TB occur?

Answer 13

When a tubercle erodes a blood vessel

Question 14

In the immunosuppressed patient, what can we see as far as tuberculosis presentation?

Answer 14

Dissemination in 10-15% of those who are mildly immune suppressed.

Dissemination in more than 50% of severely immunocompromised

Question 15

What immune cells are needed to form a granuloma?

Answer 15

T_H1

Question 16

Describe the two paths that can lead to miliary TB

Answer 16

I.

1. Primary infection –> Primary complex (localized caseation) –> progressive primary TB –> massive hematogenous dissemination –> miliary TB
2. Primary infection –> Primary complex (localized caseation) –> Latent Lesions –> Secondary TB (either by reinfection or reactivation) –> Progressive secondary TB –> massive hematogenous dissemination –> miliary TB

Question 17

What organism causes Hansen disease?

Answer 17

M. leprae

Question 18

What are the two directions an M. leprae infection can take? What determines the progression?

Answer 18

Depending on the patients cellular defensive capacity…

If intact - will progress to the tuberculoid (paucibacillary) form

If compromised - will progress to Lepromatous form

Question 19

Persons with a vigorous cellular immune response may develop the Tuberculoid form of M. leprae.

Describe the following:

1. Level of pain
2. Impact on skin
3. Nerve involvement pattern

For our purposes, what is the distinguishing aspect of this version of the disease we should use?

Answer 19

1. Painless
2. Skin lesions are limited, and they tend to be dry and hypoesthetic
3. Nerve involvement is usually asymmetric

** 5 or fewer skin lesions with absence of organisms on smears ** (to distinguish from lepromatous)

Question 20

Persons with a compromised cellular immune response may develop the lepromatous form of M. leprae.

Describe the impact of this disease on the skin.

Answer 20

•Extensive skin involvement in the cooler areas of the body, with sparing of the groin, axilla, and scalp

Question 21

How are the nerves affected in the lepromatous M. leprae progression?

What is the key aspect of this we are to use to distinguish this from the tuberculoid presentation on exam questions?

Answer 21

Nerve involvement tends to be symmetric

•6 or more lesions with possible visualization of bacilli on smear

Question 22

What is the arrow pointing to in this image?

Answer 22

A macrophage loaded with tons of M. leprae

Question 23

In which version of an M. leprae infection are skin tests with antigen from killed organisms pisitive?

Answer 23

Only in the tuberculoid form do you see a positive lepromin (Injected M. leprae antigen) result

Question 24

The Mycobacterium avium complex does not typically cause problems, but can lead to issues in immunocompromised patients. In these patients what can infection with these agents lead to?

Answer 24

Can cause pulmonary disease resembling tuberculosis, lymphadenitis, skin disease, soft tissue disease or disseminated disease

Question 25

What organism is described here?

• Gram positive filamentous bacteria
• Aerobic
• Found in soil and gingiva
• Opportunistic intracellular pathogens (replicate within cells)
• Acute, subacute, or chronic infectious disease that occurs in cutaneous, pulmonary, and disseminated forms

Answer 25

Nocardia

Question 26

What does N. asteroides cause?

Answer 26

•Pleurocutaneous nocardiosis (opportunistic respiratory infections resembling tuberculosis and CNS infections)

Question 27

What does N. brasilienses cause?

Answer 27

•Primary cutaneous nocardiosis (cellulitis, lymphocutaneous disease and actinomycetoma)

Question 28

Actinomycosis is similar to nocardosis but is anaerobic. What does it typically cause?

What are the characteristic granules associated with this bacteria called and filled with?

Answer 28

• Cause painful abscesses in the mouth, lungs, or gastrointestinal tract
• sulfur granules: filled with progeny bacteria