Microbiology - Tuberculosis/Non-TB mycobacteria - Greenblatt

Question 1

What does the Lepromin PPD test?

Answer 1

Lepromin PPD tests anti-leprosy immunocompetence, NOT exposure
tuberculoid = PPD + (why it’s called tuberculoid) = Strong immune response
lepromatous = PPD - = no immune response

Question 2

T/F: The atypical mycobacteria are environmentally-acquired infections that cause neither TB nor leprosy.

Answer 2

True

Question 3

How do atypical mycobacterial infections present?

Answer 3

Atypical mycobacterial infection in an immunocompetent adult is usually cutaneous; scrofula in children;

immunosuppressed hosts may have systemic symptoms, particularly from M. kansasii or MAI/C

Question 4

What is the slowest growing human pathogen?

Answer 4

M. leprae
–no in vitro culture system,
slowest growing human pathogen,
prefers 30C to 37C

M. leprae has an extremely long incubation period, doesn’t transmit easily, only 5-10% of humans believed susceptible to disease

Question 5

T/F: Atypical mycobacterial infections may be difficult to treat once established; require multiple antibiotics

Answer 5

True

Question 6

How does M. leprae present (two forms)?

Answer 6

Hansen’s Disease (leprosy) presents on a range from:

Tuberculoid (paucibacillary, vigorous CMI both contains infection and damages nerves, PPD+) to Lepromatous (multibacillary, weak CMI, extensive cutaneous symptoms, PPD-)

Lepromatous easily tested by skin smear, biopsy, molecular probe, serology; PPD (-)

tuberculoid may be detected by biopsy or serology but sensitivity is low – physical exam, history, PPD (+)

Question 7

When treating patients with M. Leprae, what sequelae can they develop?

Answer 7

Lepromatous patients when treated may develop erythema nodosum;
severe cases can require immunomodulant treatment like thalidomide (teratogen!)

Question 8

How is leprosy treated?

Answer 8

Treat w/ 2yrs dapsone+rifampin

Question 9

Describe the hematogenous spread of TB

Answer 9

Hematogenous spread by intracellular infection of naieve macrophages; activated ones clear it,
CD8 cells kill infected macrophages and establish caseating granulomas in which infection is contained.
TNF-alpha also important for containment

Question 10

Eradication of TB seemed possible until?

Answer 10

Eradication seemed possible until AIDS

Question 11

What is the acid fast staining procedure for TB?

Answer 11

Mycobacteria gram stain poorly, are acid-fast, very slow-growing

Acid fast staining procedure uses carbolfuchsin stain, acid/alcohol decolorization, and methylene blue counterstain; acid-fast (+)s hold carbolfuchsin during decolorization

Question 12

Which strains of TB pose the greatest public health risk?

Answer 12

MDR and XDR strains are public health nightmares

Question 13

What is the main TB transmission method?

Answer 13

Transmission is almost always to lung by inhalation, to lymph nodes, kidney, bones, CNS by hematogenous spread, to GI by swallowing infected sputum

Question 14

How are TB infections combatted in the body?

Answer 14

Immunocompetent host raises strong CMI response, can hold infection latent for decades;

Immunosenescence or immunosuppression reactivates

Question 15

What are the extrapulmonary symptoms of TB?

Answer 15

Extrapulmonary:
scrofula (fine needle aspirate),
genitourinary (intravenous urography, urine culture),
CNS (MRI, spinal tap), skeletal (MRI, joint fluid culture),
GI (Xray, CT of abdomen),
miliary (chest Xray w/ bright spotlight, lateral Xray, chest CT)

Question 16

How should the incidence of TB be most effectively reduced?

Answer 16

The most helpful factors for reducing incidence of TB in a population are good diet & housing: latent cases are not contagious

Question 17

How is TB treated?

Answer 17

Begin Directly Observed Therapy with 4-plus-drug courses featuring isoniazid; isolate patient for first two weeks.

Question 18

What is the BCG vaccine?

Answer 18

for TB
BCG vaccine (live attenuated M. bovis) is used abroad, not cost-effective here, can create weak-moderate false positive TST

Question 19

How is TB diagnosed?

Answer 19

Acid fast staining procedure

Determine exposure by TST and/or IGRA, perform antibiotic resistance testing as soon as cultures grow (~2wks for cultures, another 3wks for resistance tests)

Question 20

What are the classic TB symptoms?

Answer 20

Classic pulmonary TB (75%): cough, weight loss (“consumption”), fever, night sweats, hemoptysis, and chest pain, check sputum and chest Xray

Question 21

Why should you culture TB from gastric secretions in children?

Answer 21

They are not strong enough to cough up sufficient sputum for testing.