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USMLE Step 1: Things I Cannot Remember > Microbiology > Flashcards

Microbiology Flashcards

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USMLE® Step 1 flashcards
1
Q

What bacteria produce enzymes that inhibit protein synthesis?

A
  1. Corynebacterium diptheriae
  2. Pseudomonas aeruginosa
  3. Shigella
  4. EHEC
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2
Q

How are C. diptheriae and P. aeruginosa similar?

A

produce toxins that inactivate EF-2

  1. C. diptheriae ⇒ diptheriae toxin
  2. P. aeruginosa ⇒ exotoxin A
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3
Q

How are shigella and EHEC similar?

A

produce toxin that inactivate 60S ribosome by removing adenosine from rRNA

  1. Shigella ⇒ shiga toxin
  2. EHEC ⇒ shiga-like toxin
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4
Q

What bacteria produce toxins that increase fluid secretion?

A
  1. ETEC ⇒ heat-labile (similar to cholera toxin) & heat-stabile toxins
  2. Bacillus anthracis ⇒ edema toxin
  3. Vibrio cholerae ⇒ cholera toxin
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5
Q

What bacteria produce toxins that inhibit phagocytic ability?

A

Bordetella pertussis ⇒ pertusis toxin

  • overactivates adenylate cyclase (↑ cAMP) by disabling Gi subunit ⇒ impairs phagocytosis
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6
Q

What bacterial toxins act by inhibiting neurotransmitter release?

A
  1. Clostridium tetani ⇒ tetanus toxin
  2. Clostridium botilinum ⇒ botulinum toxin
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7
Q

What bacteria produce toxins that lyse cell membranes?

A
  1. Clostriudium perfringens ⇒ α-toxin
  2. Streptococcus pyogenes ⇒ Streptolysin O
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8
Q

What bacteria produce superantigens that cause shock?

A
  1. Staphylococcus aureus ⇒ toxic shock syndrome toxin (TSST-1)
  2. Streptococcus pyogenes ⇒ Exotoxin A
  • Binds to MHC-II and TCR outside of antigen binding site to cause overwhelming release of IL-1, IL-2, IFN-γ and TNF-α ⇒ shock
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9
Q

Where is the endotoxin found in bacterial species?

A

LPS found in most outer membrane of G(-) bacteria (both cocci and rods)

  • Edema
  • Nitric oxide
  • DIC/Death
  • Outer membrane
  • TNF-α
  • O-antigen
  • Xtremely heat-stabile
  • IL-1
  • Neutrophil chemotaxis
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10
Q

What is falsely positive in babies born to HIV(+) mothers?

A

ELISA and Western blot tests

  • falsely positives in neonates born to HIV infected mothers
    • anti-gp120 Abs cross the placenta
  • Need PCR to confirm
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11
Q

What is the extended spectrum of amoxicillin/ampicilllin?

A

G(+) & HHELPSS

  1. H. influenzae
  2. H. pylori
  3. E. coli
  4. Listeria
  5. Proteus mirabilis
  6. Salmonella
  7. Shigella
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12
Q

Which pencillin-like antibiotic is used for S. Areus?

A

Nafcillin

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13
Q

Which pencillin-like antibiotics are used for P. aeruginosa and G(-) rods?

A

Piperacillin & ticarcillin (used w/ β-lactamase inhibitors)

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14
Q

What do 1st generation cephalosporins treat?

A

PEcK

  1. Proteus mirabilis
  2. E. coli
  3. Klebsiella pneumoniae
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15
Q

What do 2nd generation cephalosporins treat?

A

HEN PEcKS

  • Haemophilus influenzae
  • Eneterobacter
  • Neisseria spp.
  • Proteus mirabilis
  • E. coli
  • Klebsiella
  • Serratia
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16
Q

What do 3rd generation cephalosporins treat?

A

Serious G (-) infections

  1. Ceftriaxone ⇒ meningitis, gonorrhea, disseminated Lyme’s disease
  2. Ceftazidime ⇒ Pseudomonas
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17
Q

What 4th generation cephalosporins treat?

A

Broad G (+) and G (-) coverage:

  • ↑ activity against P. aerigunosa
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18
Q

What do 5th generation cephalosporins treat?

A

Broad G (+) and G (-) coverage, including MRSA:

  • does not cover P. aerigunosa
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19
Q

What do monobactams cover?

A

G (-) rods only

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20
Q

List the protease inhibitors:

A

drugs ending in -navir

  • Atazanavir
  • Darunavir
  • Fosamprenavir
  • Indinavir
  • Lopinavir
  • Ritonavir
  • Saquinavir
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21
Q

What are the side effects of protease inhibitors?

A
  • Hyperglycemia
  • GI intolerance
  • Lipodystrophy
  • Nephropathy, hematuria (indinavir)
  • Rifampin (CYP/UGT inducer) is contraindicated
    • ↓ protease inhibitor concentration
22
Q

List the NRTIs:

A
  • Abacavir
  • Didanosine
  • Emtricitabine
  • Lamivudine
  • Stavudine
  • Tenofovir
  • Zidovudine
23
Q

What are the side effects of NRTIs?

A
  • Bone marrow suppression
    • reversed w/ G-CSF and erythropoietin
  • Peipheral neuropathy
  • Lactic acidosis
  • Anemia (ZDV)
  • Pancreatitis (didanosine)
24
Q

List the NNRTIs:

A
  1. Delaviridine
  2. Efavirenz
  3. Nevirapine
25
Q

What are the side effects of NNRTIs?

A
  • Rash
  • Hepatotoxicity
  • Vivid dreams and CNS symptoms (efavirenz)

Note:

  • Delaviridine & efavirenz are contraindicated in pregnancy
26
Q

List the integrase inhibitors:

A

Raltegravir

27
Q

What are the side effects of integrase inhibtors?

A

↑ creatine kinase

28
Q

List the fusion inhibitors:

A
  1. Enfuvirtide
  2. Maraviroc
29
Q

What are the side effects of fusion inhibitors?

A
  1. Enfuvirtide ⇒ skin reaction (injection site)
  2. Maraviroc ⇒ hepatic & CV problems
30
Q

When are interferons used?

A
  1. IFN-α
    • chronic Hep B & C, Kaposi sarcoma, hairy cell leukemia, condyloma acuminatum. renal cell carinoma, malignant melanoma
  2. IFN-β
    • multiple sclerosis
  3. IFN-γ
    • chronic granulomatous disease (CGD)
31
Q

What are the side effects of IFNs?

A
  1. Neutropenia
  2. Myopathy
32
Q

What can be used for Hep C therapy?

A
  1. Ribavirin (also used in RSV)
    • Inhibits synthesis of guanine nucleotides by competitively inhibiting IMP dehydrogenase
    • Toxicity ⇒ hemolytic anemia, severe teratogen
  2. Simeprevir
    • HCV protease inhibitor ⇒ prevents viral replication
    • Toxicity ⇒ Photosensitivity, rash
  3. Sofosbuvir
    • Inhibits HCV RNA-dependent RNA polymerase ⇒ chain terminator
    • Toxicity ⇒ fatigue, headache, nausea
33
Q

Pneumonia: Special Groups

  • Alcohol/IV drug abusers
  • Aspiration
  • Atypical
  • Cystic fibrosis
  • Immunocomrpomised
  • Nocosomial (hospital acquired)
  • Postviral
A
  • Alcohol/IV drug abusers
    • S. Pneumonae, Klebsiella, S. Areus
  • Aspiration
    • Anaerobes (Peptostreptococcus, Fusobacterium, Prevotella, Bacteriodes)
  • Atypical
    • Mycoplasma, Legionella, Chlamydia
  • Cystic fibrosis
    • Pseudomonas, S. Areus, S. Pneumonae
  • Immunocomrpomised
    • S. Areus, enteric gram (-) rods, fungi, viruses, P. Jirovecii (w/ HIV)
  • Nocosomial (hospital acquired)
    • S. Areus, Pseudomonas, other enteric gram (-) rods
  • Postviral
    • S. Areus, H. Influenzae, S. Pneumonae
34
Q
  1. What infections cause a brain abscess?
  2. Does site of infection predict where an abscess will form?
A
  1. Infections:
    • Most commonly viridans strep and S. Areus
    • Toxoplasma ⇒ reactivation in AIDS
    • If dental infection/extraction precedes ⇒ oral anaerobes
  2. Site of abscess:
    • Multiple abscesses ⇒ bacteremia
    • Single lesion ⇒ contigious sites
      • otitis media and mastoiditis ⇒ temporal lobe and cerebellum
      • sinusititis and dental infection ⇒ frontal lobe
35
Q

What viruses cause meningitis?

A
  • Enteroviruses (esp. Cocksackie virus)
  • HSV 1 (encephalitis)
  • HSV 2
  • HIV (also consider Cryptococcus spp.)
  • West Nile virus (also can cause encephalitis)
  • VZV
36
Q

CSF findings in meningitis:

  1. Bacterial
  2. Fungal
  3. Viral
A
  1. Bacterial
    • Opening pressure: ↑
    • Cell type: ↑ PMNs
    • Protein: ↑
    • Sugar: ↓
  2. Fungal
    • Opening pressure: ↑
    • Cell type: ↑ lymphocytes
    • Protein: ↑
    • Sugar: ↓
  3. Viral
    • Opening pressure: normal/↑
    • Cell type: ↑ lymphocytes
    • Protein: normal/↑
    • Sugar: normal
37
Q
  1. What are the ToRCHeS infections?
  2. What are the common clinical findings of these infections?
A
  1. Infections:
    • Toxoplasma gondii
    • Other: S. Agalactiae, E. Coli, Listeria, Parvovirus B19 (hydrops fetalis)
    • Rubella
    • HIV and HSV-2
    • Syphillis
  2. Common clinical findings:
    • heptasplenomegaly, jaundice, growth retardation, thrombocytopenia
38
Q

Describe Toxoplamsa gondii infection in neonates:

  • Mode of transmission
  • Maternal Manifestations
  • Neonatal manifestations
A
  • Mode of transmission
    • cat feces or ingestion of undercooked meat
  • Maternal Manifestations
    • Usually asymptomatic; lymphadenopathy (rarely)
  • Neonatal manifestations
    • ​Classic triad (chic): choriorentinits, hydrocephalus, intracranial calcifications
    • +/- “blueberry muffin” rash
39
Q

Describe Rubella infection in neonates:

  • Mode of transmission
  • Maternal Manifestations
  • Neonatal manifestations
A
  • Mode of transmission
    • Respiratory droplets
  • Maternal Manifestations
    • Rash, lymphadenopathy, arthritis
  • Neonatal manifestations
    • Classic triad: PDA (pulmonary artery hypoplasia), cataracts, deafness
    • +/- “blueberry muffin” rash
40
Q

Describe CMV infection in neonates:

  • Mode of transmission
  • Maternal Manifestations
  • Neonatal manifestations
A
  • Mode of transmission
    • sexual contact, organ transplant
  • Maternal manifestations
    • usually asymptomatic; mononucleosis-type illness
  • Neonatal manifestations
    • seizures
    • petechial rash
    • periventricular calcifications
    • hearing loss
    • “blueberry muffin” rash
41
Q

Describe HIV infection in neonates:

  • Mode of transmission
  • Maternal manifestations
  • Neonatal manifestations
A
  • Mode of transmission
    • sexual contact, needlestick
  • Maternal manifestations
    • variable depending on CD4 count
  • Neonatal manifestations
    • recurrent infections
    • chronic diarrhea
42
Q

Describe HSV-2 infection in neonates:

  • Mode of transmission
  • Maternal manifestations
  • Neonatal manifestations
A
  • Mode of transmission
    • skin or mucous membrane contact
  • Maternal manifestations
    • usually asymptomatic; herpetic (vesicular) lesions
  • Neonatal manifestations
    • encephalitis
    • herpetic (vesicular) lesions
43
Q

Describe Syphillis infection in neonates:

  • Mode of transmission
  • Maternal manifestations
  • Neonatal manifestations
A
  • Mode of transmission
    • sexual contact
  • Maternal manifestations
    • Chancre (1°) and disseminated rash (2°) - stages most likely to result in fetal infection
  • Neonatal manifestations
    • often results in stillbirth, hydrops fetalis
    • If child survives:
      • facial abnormalities (notched teeth, saddle nose, short maxilla)
      • saber shins
      • CN 8 deafness
44
Q

Bacteria with a branching filamentous appearance:

A
  • Actinomyces (G+)
  • Nocardia (weakly acid-fast)
45
Q

Bacteria with a pleomorphic appearance:

A
  • Chlamydiae (Giesma)
  • Ricketssiae (Giesma)

These are both G- bacteria but cannot be viewed on gram stain

46
Q

Spiral bacteria:

A

Spirocetes (G-):

  • Borrelia (Giesma)
  • Leptospira
  • Treponema
47
Q

Bacteria with no cell wall:

A
  • Mycoplasma
  • Ureaplasma (contains sterols)
48
Q

Bacteria that cannot be viewed on Gram stain:

A

These Microbes May Lack Real Color

  • Treponema
  • Mycobacteria
  • Mycoplasma
  • Legionella
  • Ricketssia
  • Chlamydia
49
Q

Stains:

  • Giesma
  • PAS (periodic acid-Schiff)
  • Ziehl Neelsen
  • India ink
  • Silver stain
A
  • Giesma:
    • Chlamydia, Borrelia, Ricketssia, Trypanosomes, Plasmodium
  • PAS (periodic acid-Schiff): stain glycogen, mucopolysaccharides
    • Diagnoses Whipple disease (Tropheryma whipplei)
  • Ziehl Neelsen (carbol fuschin):
    • acid fast bacteria (Norcardia, Mycobacteria)
    • protozoa (Cryptosporidium oocysts)
  • India ink:
    • Cryptococcus neoformans
  • Silver stain:
    • Fungi (e.g. Pneumocystis)
    • Legionella
    • H. Pylori
50
Q

Special Culture Requirements:

  1. H. Influenzae ⇒
  2. Neisseria ⇒
  3. Bordetella pertussis ⇒
  4. C. Diphtheriae ⇒
  5. M. tuberculosis ⇒
  6. M. pneumonia ⇒
  7. Lactose-fermenting enterics ⇒
  8. E. coli ⇒
  9. Legionella ⇒
  10. Fungi ⇒
A
  1. H. Influenzae ⇒ Chocolate agar
    • ​​Factors V (NAD+) and X (hematin)
  2. Neisseria ⇒ Thayer-Martin agar
    • ​​Vancomycin, Trimethoprin, Colistin, Nystatin
  3. Bordetella pertussis ⇒ Bordet-Gengou agar, Regan-Lowe medium
  4. C. Diphtheriae ⇒ Tellurite agar, Löffler medium
  5. M. tuberculosis ⇒ Löwenstein-Jensen agar
  6. M. pneumonia ⇒ Eaton agar (requires cholesterol)
  7. Lactose-fermenting enterics ⇒ MacConkey agar
    • fermentation produces acid, causing colonies to turn pink
  8. E. coli ⇒ Eosin-methylene blue
    • colonies w/ metallic green sheen
  9. Legionella ⇒ silver stain
    • Charcoal yeast extract agar buffered with cysteine and iron
  10. Fungi ⇒ Sabouraud agar
51
Q
A

USMLE Step 1: Things I Cannot Remember (16 decks)

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