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USMLE > Microbiology - Antimicrobials > Flashcards

Microbiology - Antimicrobials Flashcards

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USMLE® Step 1 flashcards
1
Q

What are the 4 major sites of antibacterial activity in the bacterial cell?

A
  1. Inhibitors of cell wall synthesis
  2. Inhibitors of protein synthesis
  3. Inhibitors of DNA/RNA synthesis
  4. Inhibitors of folic acid reduction
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2
Q

How does Penicillin work and what organisms is it typically used for?

A

Blocks peptidoglycan cross-linking.

Used against gram positive organisms, some gram negative (n. meningitidis) and spirochetes (t. pallidum).

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3
Q

How does Ampicillin/Amoxicillin work and what organisms is it typically used for?

A

Blocks peptidoglycan cross-linking and is penicillinase resistant.

“HHELPSS” penicillin

H. influenzae, H. pylori, E. coli, L. monocytogenes, P. mirabilis, Salmonella, Shigella.

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4
Q

List the beta-lactamase inhibitors.

A

“CAST”

Clavulanic acid, Avibactam, Sulbactam, Tazobactam.

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5
Q

Organisms not covered by the 1st-4th Generation Cephalosporins are?

A

“LAME”

Listeria, Atypicals (Chlamydia, Mycoplasma), MRSA, Enterococci

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6
Q

How do 1st Generation Cephalosporins work and what organisms are they typically used for?

A

Inhibit cell-wall synthesis. Less susceptible to Penicillinases.

Gram positive + PEcK

Proteus, E. coli, Klebsiella

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7
Q

How do 2nd Generation Cephalosporins work and what organisms are they typically used for?

A

Inhibit cell-wall synthesis. Less susceptible to Penicillinases.

Gram positive + HENS PEcK

H. influenza, Enterobacter aerogenes, Neisseria, Serratia
Proteus, E. coli, Klebsiella

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8
Q

How do 3rd/4th Generation Cephalosporins work and what organisms are they typically used for?

What property do they have over 1st and 2nd gen?

A

Inhibit cell-wall synthesis. Less susceptible to Penicillinases.

3rd Gen can cross BBB - meningitis
Both add cover of Pseudomonas.

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9
Q

What do 5th Generation Cephalosporins cover?

A

Listeria, MRSA, Enterococcus faecalis.

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10
Q

Cephalosporins increase the nephrotoxicity of?

A

Aminoglycosides.

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11
Q

Monobactams are good only for?

A

Gram negative bacilli.

Synergistic with aminoglycosides.

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12
Q

Vancomycin is only good for?

What are the common adverse effects?
What is an uncommon adverse effect?

A

Gram positive bacteria only, including MRSA.

Nephrotoxicity, Ototoxicity, Thrombophlebitis.
Red man syndrome (give slowly and with histamine)

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13
Q

What is the mechanism of Vancomycin resistance?

A

Enterococcus modifies AAs to D-Ala-D-Ala to D-Ala-D-Lac

“Pay back 2 D-Alas for Vandalising Vancomycin”

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14
Q

Where do the protein synthesis inhibitors work?

List them.

A

Specifically target the small bacterial ribosome (70S; made of 30S and 50S), leaving human ribosome 80S unaffected.

buy AT 30, CEL at 50

Aminoglycosides, Tetracyclines
Chloramphenicol, Clindamycin, Erythromycin, Linezolid.

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15
Q

What are the common Aminoglycosides?

How do they work?

What are the common side effects?

A

“mean GNATS cNNOT kill anaerobes”

Gentamicin, Neomycin, Amikacin, Tobramycin, Streptomycin.
Bactericidal inhibition of 30S ribosomal subunit.
Nephrotoxicity, NM blockade, Ototoxicity, Teratogen.

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16
Q

Which antibiotic is useful in renal failure and why?

A

Doxycycline.

It is faecally eliminated.

17
Q

How do Macrolides work?

What are their adverse effects?

A

Azithromycin, Clarithromycin, Erythromycin.

Inhibit protein synthesis by blocking translocation; bacteriostatic.

MACRO:
Motility issues, Arrhythmia due to long QT, Cholestasis, Rash, Eosinophilia.

18
Q

What are the anti-mycobacterial drugs?

How is Leprosy treated?

A

“RIPE for treatment”

Rifampin, Isoniazid, Pyrazinamide, Ethambutol.

Add Dapsone and Rifampin +/- Clofazimine for Leprosy.

19
Q

What are the Rifamycins and how do they work?

What are the 4 Rs of Rifampin?

A

Rifampin, Rifabutin.

RNA polymerase inhibitor
Ramps up cytochrome pP-450
Red/Orange body fluids
Rapid resistance if used alone

Rifampin ramps up cytochrome P-450 but Rifabutin does not.

20
Q

What is the mechanism of action of Isoniazid?

What are its clinical uses?

What are the adverse effects and what special step should be taken?

A

Reduces synthesis of mycolic acids.

Can treat TB and is the only agent for prophylaxis.

INH Injures Neurons and Hepatocytes so administer with B6 (pyridoxine).

21
Q

Which antibiotic, and for which bug, would you give an HIV+ patient with a CD4+ count of less than 200?

A

TMP-SMX

Pneumocystis pneumonia

22
Q

Which antibiotic, and for which bug, would you give an HIV+ patient with a CD4+ count of less than 100?

A

TMP-SMX

Pneumocystis pneumonia and toxoplasmosis

23
Q

Which antibiotic, and for which bug, would you give an HIV+ patient with a CD4+ count of less than 50?

A

Azithromycin or Clarithromycin

Mycobacterium avid complex.

24
Q

How does Amphotericin B work?

What are the common side effects?

A

“AmphoTEARacin”

Binds ergosterol (unique to fungi); forms (tears) membrane pores that leak electrolytes.

“Shake and Bake” + Nephrotoxicity + Arrhythmias

25
Q

How do the fungal “Azoles” work?

What is the common side effect?

A

Inhibit fungal ergosterol synthesis by inhibiting the cytochrome P-450 enzyme that converts lanosterol to ergosterol.

Testosterone synthesis is inhibited. Liver dysfunction.

26
Q

How does Chloroquine treat infection with Plasmodium?

How are some Plasmodium app. resistant?

A

Blocks detoxification of Heme into Hemozoin. Heme accumulates and is toxic to Plasmodia.

Falciparum has a membrane pump for efflux. So Atovaquone is used.

27
Q

What class of antimicrobials are Oseltamivir and Zanamivir?

How do they work?

A

Both are antivirals for Influenza.

They target neuraMInidase; preventing release of progeny viruses from infected cells.

28
Q

What class of antimicrobials are the …clovirs?

(Acyclovir, Famciclovir, Valacyclovir, Ganciclovir)

Which viruses can they be used for?

A

They are guanosine analogs that preferentially inhibit viral DNA polymerase.

Acyclovir, Famciclovir, and Valacyclovir = HZV and VZV

Ganciclovir = CMV.

29
Q

Ideal HAART therapy consists of?

A

3 agents.

Ideally 2 nucleotide reverse transcriptase inhibitors and one integrate inhibitor.

30
Q

…navir indicates what sort of anti-viral medication?

…tegr… indicates what sort of anti-viral medication?

A

“Navir tease a protease” (Protease inhibitors)

Integrase inhibitors.

31
Q

How do alcohol and Chlorhexidine sterilise?

A

Denature proteins and disrupt cell membranes.

Not sporicidal.

32
Q

How do Hydrogen Peroxide and Iodine work as disinfectants/sterilisers?

A

Hydrogen peroxide causes free radical damage and is sporicidal.

Iodine halogenates DNA, RNA, and proteins. It may be sporicidal.

33
Q

What are the antibiotics to avoid in pregnancy?

A

“SAFe Children Take Really Good Care”

Sulfonamides (kernicterus)
Aminoglycosides (Ototoxicity)
Fluoroquinolones (Cartilage damage)
Clarithromycin (Embryotoxic)
Tetracyclines (Discoloured teeth, inhibition bone growth)
Ribavirin (Teratogenic)
Griseofulvin (Teratogenic)
Chloramphenicol (Grey baby syndrome)

USMLE (14 decks)

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