Mycos (-plasma, -bacterium)

Question 1

What characterizes mycobacterium structurally?

Answer 1

Acid-fast –> due to high lipid laden walls. Cell walls don’t dissolve in acid, so red stain doesn’t wash off. “Fast red car” –> acid fast organisms stain red.

Question 2

What is mycolic acid?

Answer 2

Large fatty acid bound to carbohydrate, forming a glycolipid. Found in mycobacterium tuberculosis.

Question 3

What is cord factor?

Answer 3

In virulent strains of mycobacterium tuberculosis, inhibits macrophage maturation and induces release of TNF-alpha.

Question 4

What are sulfatides?

Answer 4

In mycobacterium tuberculosis, inhibits phagolysosomal fusion, facilitates intracellular survival.

Question 5

What population does mycobacterium avium intracellulare cause disease in?

Answer 5

AIDs patients with CD4 count < 50.

- Disseminated infection with fever, weight loss, hepatitis, and diarrhea.

Question 6

What ppx is there for MAI?

Answer 6

Azithromycin with CD4 count >50.

Question 7

What population does mycobacterium scrofulaceum cause disease in?

Answer 7

cervical lymphadenitis in children.

Question 8

What population does mycobacterium marinum cause disease in?

Answer 8

Hand infection in aquarium handlers.

Question 9

What is Hansen disease caused by?

Answer 9

Mycobacterium leprae.

Question 10

In what temperature does M. leprae grow best in?

Answer 10

Cool temperatures - infects skin and superficial nerves - glove/stocking loss of sensation. Cannot be grown in vitro.

Question 11

What is the reservoir of M. leprae in the US?

Answer 11

armadillos

Question 12

What is the presentation of lepromatous form of M. leprae?

Answer 12

Presents diffusely over the skin, with lionlike facies - contagious.

Question 13

What is the immune response to lepromatous form of M. leprae?

Answer 13

Low cell-mediated immunity, humoral th2 response.

Question 14

What is the presentation of the tuberculoid form of M. leprae?

Answer 14

Few hypoesthetic, hairless skin plaques.

Question 15

What is the immune response to the tuberculoid form of M. leprae?

Answer 15

High cell-mediated immunity with largely Th1 type immune response.

Question 16

What is the treatment for tuberculoid form of M. leprae?

Answer 16

Dapsone, rifampin.

Question 17

What is the treatment for lepromatous form of M. leprae?

Answer 17

Dapsone, rifampin, clofazimine.

Question 18

What is special about the structure of mycoPLASMAS?

Answer 18

No cell wall - not seen on gram stain! Pleomorphic - round to oblong shaped. Very small (smaller than some viruses). Bacterial wall contains sterols for stability.

Question 19

What do mycoplasmas need to grow?

Answer 19

Cholesterol required for membrane synthesis. Eaton Agar.

Question 20

Why is penicillin ineffective against mycoplasmas?

Answer 20

No cell wall.

Question 21

What kind of hemolysis does Mycoplasma cause?

Answer 21

Cold agglutins; IgM. Binds to “I” antigen of RBCs at cold temperatures. 1st or 2nd week of mycoplasma infection.

Question 22

What does Mycoplasma pneumoniae classically cause?

Answer 22

“Walking” pneumonia: insidious onset, headache, non-productive cough, patchy/diffuse interstitial infiltration that looks worse on Xray than the patient looks.

Question 23

In what patients is M. pneumoniae infection more common?

Answer 23

Patients <30 yrs old.

Military recruits, prisons.

Question 24

What is the treatment for M. Pneumoniae?

Answer 24

macrolides, doxycycline, or fluoroquinolones.

Question 25

What organism can cause non-gonococcal urethritis with yellow mucoid discharge from the urethra?

Answer 25

Ureaplasma urealyticum.

Question 26

What does ureaplasma require for growth?

Answer 26

Cholesterol and urea. Urease metabolizes urea into ammonia and CO2.