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USMLE > Microbio > Flashcards

Microbio Flashcards

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USMLE® Step 1 flashcards
1
Q

What is the pathogenic mechanism for Shigella infection

A

Mucosal invasion of M cells

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2
Q

Three vulnerable populations for Shigella

A

Kids
men who have sex with men
adults in nursing facilities

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3
Q

The host inflammatory response against Shigella is largely mediated by

A

Neutrophils

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4
Q

What best explains lack of protective immunity agaiinst Neisseiria infections?

A

High variability of microbial surface antigenic structure

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5
Q

The Hib vaccine protects against

A

Encapsulated Haemophilus influenza meningitis

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6
Q

Non-encapsulated H influenzae cause

A

otitis media, sinusitis and bronchitis in little children

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7
Q

which part of the US is Blastomyces dermatitidis found?

A

Mississippi and Ohio River valleys

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8
Q

Symptoms of Blastomyces infection in immunocompetent

A

granuloma formation, mimics pneumonia

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9
Q

Mucor species is characteristic of patients with

A

neutropenia, burns or diabetes mellitus (diabetic ketoacidosis)

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10
Q

Risk factors for pneumocystis jirovecii infection in HIV pt

A

CD4 <200; oropharyngeal candidiasis

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11
Q

Prophylaxis for pneumocystitis jirovecii infection in HIV pt

A

Trimethoprim-sulfamethoxazole

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12
Q

Risk factors for Toxoplasma gondii infection in HIV pts

A

CD4 <100

Positive Toxoplasma IG antibody

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13
Q

Prophylaxis for Toxoplasma gondii in HIV pts

A

Trimethoprim-sulfamethoxazole

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14
Q

Risk factor for Mycobacterium avium infection in HIV pt

A

CD4 <50

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15
Q

Prophylaxis against Mycobacterium avium in HIV pt

A

Azithromycin

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16
Q

Risk factor for Histoplasma capsulatum infection in HIV pts

A

CD4 <150

Ohio and Mississippi river valley

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17
Q

Prophylaxis for Histoplasma infection in HIV pts

A

Itraconazole

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18
Q

How to distinguish TB infection from Mycoplasma avium complex infection in HIV patient?

A

MAC more likely presents with reticuloendothelial symptoms like hepatosplenomegaly, elevated alkaline phosphatase and LDH and anemia; grows best at 41C

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19
Q

What is the major virulence factor for Haemohphilus influenzae type b?

A

Polyribosylribitol phosphate (PRP) capsule that binds H1 and prevents complement deposition

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20
Q

How does diphtheria exotoxin function

A

Inhibits protein synthesis by ADP-ribosylation (inhibition) of intracellular EF-2

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21
Q

what does Diphtheria toxin cause morphologically

A

Respiratory cell necrosis with formation of fibrinous, coagulative exudates

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22
Q

Degradation of lecithin by lecithinase is a function of which pathogen

A

C. perfringens (causes gas gangrene)

23
Q

Shiga toxin (Shigella) and Shiga-like toxin (EHEC) causes protein synthesis inhibition by

A

inactivation of 60s ribosomal subunit

24
Q

How does pertussis AB exotoxin function

A

Catalyzes ribosylation of G protein alpha1 subunits leading to increased cAMP production.

25
Q

Consequences of Pertussis exotoxiin

A

Increased insulin production, lymphocyte and neutrophil dysfunction and increased sensitivity to histamine

26
Q

Example of a selective medium

A

Thayer-Martin VCN (identify Neisseiria species and fungi)

27
Q

Example of differential media

A

MacConkey agar and Eosin methylene blue to culture enteric organisms (ferment lactose- pink on M, black on E)

28
Q

Example and purpose of reducing media

A

Thioglycolate broth, culture anaeorbic organisms

29
Q

What is the major virulence factor for Strep pyogenes

A

Protein M; inhibits phagocytosis and activation of complement

30
Q

Most common cause of retinitis in HIV-positive patients

A

CMV

31
Q

Treatment for CMV retinitis

A

Gancliclovir (guanine nucleoside analog with greater activity against CMV DNA polymerase)

32
Q

Clarithromycin treatment for HIV patients

A

Mycobacterium avium complex

33
Q

Flucytocine treats

A

Fungal infections including cryptococcal infections

34
Q

Treats hepatitis B and C, hairy cell leukemia, condyloma acuminatum and Kaposi’s sarcoma

A

Leukocyte interferon alpha

35
Q

Treats pneumocystis pneumonia

A

Pentamidine

36
Q

Which cells play a key role in Myocobacterium tuberculosis infection?

A

CD4+ T cells, which recruit macrophages that form Langhans giant cells (have multple nuclei organized in shape of horseshoe)

37
Q

Acute treatment of Corynebacterium diptheriae

A
  1. Diptheria antitoxin (passive immunization)
  2. Penicillin or erythromycin
  3. DPT vaccine
38
Q

The clinical consequence of C. diptheria are due to

A

Exotoxin

39
Q

S. Aureus uses this enzyme to activate prothrombin, convert fibrinogen to fibrin and protect itself against phagocytosis

A

Coagulase

40
Q

Lecithinase (alpha toxin) is the major virulence factor for which pathogen

A

C. perfringens

41
Q

Has phospholipase C activity that increases platelet aggregation and adherence molecule expression on leukocytes and endothelial cells, causing vasocclusion and necrosis of affected tissues

A

Lecithinase (alpha toxin) of C. perfringens

42
Q

Oral thrush, interstitial pneumonia and severe lymphopenia in first year of life suggests

A

Vertical transmission of HIV from mother to child

43
Q

Treatment for HIV pregnant woman to avoid vertical transmission

A

2 Reverse transcriptase inhibitors + protease inhibitor/non-nucleoside RT inhibitor, or integrase inhibitor

44
Q

Which anti-HIV therapy is teratogenic?

A

Efavirenz in first 8 weeks

45
Q

Zidovudine usage in infants is for

A

HIV prophylaxis if they were born to HIV-infected mothers

46
Q

NRTI therapy that is associated with hypersensitivity reaction in individuals with HLA-B*57:01 allele

A

Abacavir

47
Q

NNRTIs associated with Stevens-Johnson syndrome and toxic epidermal necrolysis and abnormal LFTs

A

Efavirenz and Nevirapine

48
Q

NRTI associated with asymptomatic macular rash on palms or soles

A

Emtricitabine

49
Q

HIV therapy that causes hyperglycemia, GI symptoms and lipodystrophy

A

Protease inhibitors (lopinavir)

50
Q

White patches on retina in patient with pneumocystis pneumonia implies

A

CMV retinitis (pts with CD4 <50)

51
Q

Standard tx for Chlamydia

A

Macrolide (azithromycin– protein synthesis inhibitor) and Cephalosporin

52
Q

Why is probenecid co-administered with Penicillin in treatment of neurosyphillis or gonorrhea?

A

Inhibits organic ion transporters in kidney and renal tubular secretion of Penicillin– Increases penicillin serum concentration

53
Q

Function of M protein on Streptococcus bacteria

A

Prevents opsonization and destruction by complement

54
Q

Function of Protein A in Staph Aureus

A

Binds Fc of immunogloblulins to prevent opsonization

USMLE (36 decks)

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