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Clinical Microbio > Antimicrobials > Flashcards

Antimicrobials Flashcards

1
Q

Define Minimum Inhibitory Concentration (MIC)

A

lowest concentration of an antimicrobial agent that prevents visible growth in agar or broth dilution susceptibility test

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2
Q

Define breakpoint

A
  • MIC or zone diameter value used to indicate susceptible (S), intermediate (I), and resistant (R)
  • some labs report NI (not interpreted) if no established breakpoint
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3
Q

Define the efficacy ratio

A
  • divide resistant breakpoint MIC by the MIC obtained by broth dilution
  • tool to evaluate relative efficacy of different antimicrobial drugs
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4
Q

Which antimicrobials are considered broad spectrum?

A
  • tetracyclines
  • phenicols
  • quinolones
  • 3rd- and 4th-generation cephalosporins
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5
Q

What antimicrobials are considered narrow spectrum?

A
  • Glycopeptides & bacitracin (G+)
  • Polymixins (G-)
  • Aminoglycosides & sulfonamides (aerobes)
  • Nitroimidazoles (anaerobes)
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6
Q

What is the MOA of beta-lactams?

A
  • target and bind to penicillin-binding proteins (PBPs), inhibiting bacterial cell wall synthesis
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7
Q

What is the bacterial mechanism of resistance to beta-lactams?

A
  • enzymatic destruction of beta-lactam rings
  • target PBP modification
  • reduced intracellular accumulation
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8
Q

What is the MOA of glycopeptides?

A

inhibit the last stages of cell wall assembly by preventing cross-linking reactions

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9
Q

What is the bacterial mechanism of resistance to glycopeptides?

A
  • target modification
  • production of false targets
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10
Q

What is the MOA of quinolones?

A

targets DNA gyrase and topoisomerase IV of the bacteria and inhibits the necessary step of supercoiling

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11
Q

What is the bacterial mechanism of resistance to quinolones?

A
  • target modification
  • reduced intracellular accumulation
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12
Q

What is the MOA of aminoglycosides?

A

target and bind to the 30s ribosomal subunit to cause misreading of the genetic code which results in inhibition of protein synthesis

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13
Q

What is the bacterial mechanism of resistance to aminoglycosides?

A
  • antibiotic (structural) modification
  • target modification
  • reduced uptake
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14
Q

What is the MOA of macrolides?

A

target and bind to 50S ribosomal subunit to inhibit translocation and transpeptidation process, resulting in inhibition of protein synthesis

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15
Q

What is the bacterial mechanism of resistance to macrolides?

A
  • reduced intracellular uptake
  • target modification
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16
Q

What is the MOA of tetracyclines?

A

target and bind to 30S ribosomal subunit to prevent aminoacyl-tRNA to attach to RNA-ribosome complex, inhibiting protein synthesis

17
Q

What is the bacterial mechanism of resistance to tetracyclines?

A
  • reduced intracellular accumulation
  • target modification
18
Q

What is the MOA of rifampin?

A

interacts with the beta-subunit of the bacterial RNA polymerase to block RNA synthesis

19
Q

What is the bacterial mechanism of resistance to rifampin?

A
  • target modification
20
Q

What is the MOA of sulfonamides?

A

targets dyhydropteroate synthase (DHPS) and prevents addition of para-aminobenzoic acid (PABA), inhibiting folic acid synthesis

21
Q

What is the bacterial mechanism of resistance to sulfonamides?

A
  • target modification
22
Q

What are some examples of narrow-spectrum aminoglycosides?

A
  • streptomycin and dihydrostreptomycin
    • active against aerobic gram neg
23
Q

What are some expanded spectrum aminoglycosides?

A
  • neomycin, kanamycin
    • active against several gram pos and many gram neg aerobes
  • gentamicin, amikacin
    • extended spectra that includes Pseudomona aeruginosa
24
Q

What are aminoglycosides used for?

A
  • control local and systemic infections caused by aerobic bacteria (generally gram neg)
    • e.g. septicemia; tracheobronchitis, pneumonia, osteoarthritis, infections of urinary tract
  • potential for nephrotoxicity so contraindicated if plasma creatinine (>5 mg/dL)
25
Q

Describe the spectrum of penicilin G

A
  • narrow spectrum
    • most aerobic/anaerobic gram pos
    • few gram neg - Pasteurella multocida, Clostridium spp.
26
Q

What are two broad-spectrum semisynthetic penicillins and what do they target?

A
  • Ampicillin
    • gram pos (Strep, sensitive Staph, most Clostridia)
    • some gram neg (E. coli, Salmonella, Pasteurella)
  • Amoxicillin
    • slightly better activity vs. Gram negs
    • most anaerobic bacteria sensitive
27
Q

Describe the spectrum of Clavulanate-potentiated amoxicilin (Clavamox)

A
  • combines B-lactamase inhibitors and broad-spectrum penicillins that increase spectrum and efficiency
  • active against gram + and gram -
    • e.g. ​Staph, Strep, Corynebacterium, Clostridium, Escherichia, Kleb, Shigella
28
Q

What are some examples of 1st generation cephalosporins? What microbes are susceptible to them?

A
  • Cefazolin, Cephalexin
  • mainly gram + cocci
29
Q

What are some examples of 2nd generation cephalosporins? What microbes are susceptible to them?

A
  • Cefaclor, Cefoxitin
  • E. coli, Kleb, Proteus; not first choice for gram +
30
Q

What are some examples of 3rd generation cephalosporins? What bacteria are susceptible to them?

A
  • Cefpodoxime, Cefovecin, Ceftazidime, Ceftiofur
  • Enterobacteriaceae, Pseudomonas, Staph aur, Strep pyogenes
31
Q

What are some examples of 4th generation cephalosporins?

A
  • Cefepime, Cefpirome
  • more resistant against some beta-lactamases
32
Q

What are some examples of tetracyclines? What is their spectrum?

A
  • Tetracycline, doxycycline oxytetracycline, chlortetracycline
  • Broad spectrum: gram + and gram -, some anaerobes, Chlamydia, mycoplasmas, some protozoa, Rickettsiae (Anaplasma, Ehrlichia)
33
Q

Describe fluoroquinolones

A
  • Enrofloxacin, Ciprofloxacin, Difloxacin, Orbifloxacin, Marbofloxacin
  • Synergistic effect w/ B-lactams, aminoglycosides, clindamycin, metronidazole
  • “second-line drug” - DO NOT use prophylactically or for anaerobes
  • **serious infections and short term therapy only**
34
Q

What is the spectrum of quinolones?

A
  • Broad spectrum against most Gram - bacteria and some Gram +
  • particularly effective against Gram - enteric pathogens and Pseudomonas spp.

​​*only drugs effective vs. Pseudomonas that can be given orally*

NOT effective against anaerobes

35
Q

Which antimicrobials should you use for deep-seated infections and intracellular pathogens?

A

fluoroquinolones

36
Q

Which drug class should not be used in immature animals?

A

Fluoroquinolones - high prolonged dosages in growing dogs produce cartilaginous erosions –> lameness

37
Q

What are some signs of quinolone toxicity?

A

Seizures, retinal blindness (cats), increased liver enzymes, GI upset

38
Q

What is the spectrum for macrolides?

A
  • active against most aerobic and anaerobic G+
  • some Gram - (Tilmicosin):Mannheimia, Pasteurella
  • Mycobacterium, Mycoplasma, Chlamydia, and Rickettsia
39
Q

What are some examples of Lincosamides and what are they effective against?

A
  • Clindamycin and Lincomycin
    • Strep, Staph
    • Anaerobic organisms, bacteroides, fusobacterium, C. perf, Actinomycese sp.

Clinical Microbio (11 decks)

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