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Microbiology Exam 1 > Antibiotics > Flashcards

Antibiotics Flashcards

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1
Q

Antibiotic Susceptibility Testing: Bactericidal Activity

A
  • Level of antimicrobial activity that KILLS

- Lowest concentration of antibiotic that kills 99.9% = minimum bactericidal concentration (MBC)

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2
Q

Antibiotic Susceptibility Testing: Bacteriostatic Activity

A
  • Level of antimicrobial activity that INHIBITS GROWTH

- Lowest concentration of antibiotic that inhibits growth = minimum inhibitory concentration (MIC)

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3
Q

Antibiotic

A

Isolated in NATURE

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4
Q

Antimicrobial

A

Synthesized in a LAB

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5
Q

Bacteriostatic

A

Inhibit growth

***Used when host defenses can be counted on

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6
Q

Bactericidal

A

Killing

***Used during invasive infection: bacteremia, meningitis, endocarditis

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7
Q

Broad-Spectrum Antibiotic (Definition and Advantages/Disadvantages)

A

Effective against a large variety of bacteria

Advantage: increased likelihood of effectiveness agaisnt bacterial infection of UNKNOWN etiology

Disadvantage: increased likelihood of disrupting normal biota

***Prescribed when you are unsure of the bacteria that is infection and want to start treatment immediately

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8
Q

Narrow-Spectrum Antibiotic (Definition and Advantages/Disadvantages)

A

Effective against only a small subset of bacteria

Advantage: avoids disruption of the normal microbiota

Disadvantage: Must have SPECIFIC DISEASE causing bacteria identified in order to choose abx

***Used in non-emergent cases

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9
Q

Do antibiotics cause antibiotic resistance?

A

No; they select against sensitive bacteria and for resistant bacteria, which allows for survival of bacteria that have gained a rare mutation/genetic acquisition

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10
Q

Empiric Therapy

A

Generally BROAD SPECTRUM

-Treatment while waiting for lab results

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11
Q

Targeted Therapy

A

NARROW SPECTRUM

-Refined treatment

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12
Q

Antibiotic resistance is ____ at an alarming rate; Antibiotic discovery is ____ at an alarming rate

A

Accelerating; Decelerating

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13
Q

Antibiotic Resistance (General Mechanisms)

A
  1. Breakdown of an antibiotic (e.g. Hydrolysis)
  2. Chemical modification of an antibiotic (e.g. Methylation or Phosphorylation)
  3. Alteration of the Target (Mutations and/or gene acquisition)
  4. Altered permeability, decreased influx, or increased efflux (e.g. pumps to pump out abx)
  5. Lack of target
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14
Q

Minimum Inhibitory Concentration (MIC) tests

A
  1. Disk-diffusion assay (e.g. Kirby-Bauer Test)
    - Abx migrates out from disc from high concentration to low concentration; can measure zone of inhibition/clearing to get MIC
  2. E-Test (same thing, except with strips that have a tapering of high to low concentration of abx)
  3. Broth Culture (measures both MIC and MBC; see subsequent slide)
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15
Q

Broth Culture

A

Measures both MIC and minimum bactericidal concentration (MBC)
-Measures DENSITY of bacteria based on how much light comes through the test tube

***MIC measures inhibition of growth via visualization in test tube

***MBC measures killing of bacteria via growth (or lack of growth) on an agar

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16
Q

Cell Wall Active vs Membrane Active Antibiotics

A

Cell Wall Active:

  • Disrupts PEPTIDOGLYCAN synthesis
  • ONLY effective against ACTIVELY DIVIDING bacteria

Membrane Active:

  • Disrupts or interferes with MEMBRANE integrity/synthesis
  • Effective against RESTING AND ACTIVELY DIVIDING bacteria
17
Q

Beta-lactams

A
  • Bactericidal*
  • Inhibit cell wall synthesis

e.g. Penicillins,Cephalosporins, Cephamycins, Carbapenems, Monobactams

18
Q

Beta-Lactams (Mechanism of Action)

A

Bind the active site transpeptidases (i.e. Penicillin Binding Proteins (PBP)), preventing them from crosslinking peptidoglycan together

19
Q

Resistance to Beta-Lactams (4 mechanisms)

A
  1. Altered transpeptidases (e.g. mutation: decreased abx affinity)
  2. Altered outer-membrane permeability (e.g. mutation in porins)
  3. Presence of efflux pumps
  4. Chemical modificaiton of antibiotic (Beta-Lactamase)
20
Q

Vancomycin (Sensitive Bacteria)

A

Bactericidal

  • Vancomycin binds two D-ala residues on the end of the peptide chains, PREVENTING them from interacting with TRANSPEPTIDASE
  • Cross-links cannot be formed = cell death
21
Q

Vancomycin (Resistant Bacteria)

A
  • The last D-ala has been REPLACED by a D-LACTATE, so Vancomycin cannot bind
  • Cross-links are formed and cell wall is successfully made
22
Q

Bacitracin

A
  • Bactericidal*
  • Interferes with dephosphorylation in cycling of lipid carier that transfers peptidoglycan subunits to the growing cell wall
23
Q

Protein Synthesis Inhibitors (3 of them)

A

Tetracyclines, Aminglycosides, Macrolides

24
Q

Tetracycline

A
  • Bacteriostatic*
  • Broad Spectrum
  • Bind 30s subunit
    e. g. Tetracycline, Doxycycline

Mnemonic: Both have cycline in the name

25
Q

Aminoglycosides

A
  • Bactericidal*
  • Oxygen-dependent (INEFFECTIVE against intestinal pathogens)
  • Bind 30s subunit
    e. g. Gentamicin, Kanamycin
26
Q

Macrolides

A
  • Bacteriostatic*
  • Used as an alternative for penicillin allergies
  • Bind 50s subunit
    e. g. Erythromycin, Azithromycin
27
Q

Nucleic Acid Synthesis Inhibitors (3 of them)

A

Quinolones, Rifampin/Rifabutin, Metronidazole

28
Q

Quinolones

A
  • Bactericidal*
  • WIDELY USED
  • MOA: inhibits DNA replication, recombination, and repair via DNA topoisomerase type II (gyrase) or topoisomerase type IV
29
Q

Rifampin/Rifabutin

A
  • Bactericidal*

- MOA: binds to DNA-dependent RNA polymerase and inhibits initiation of RNA synthesis

30
Q

Metronidazole

A
  • Bactericidal*

- MOA reduced by bacteria = toxic compounds that damage DNA

31
Q

Antimetabolites (MOA and examples)

A

Bacteriostatic

MOA: Target folate metabolism, preventing synthesis of purines and thymidine, and ultimately preventing DNA/RNA synthesis

e.g. Sulfonamides and Trimethoprim (***Work together SYNERGISTICALLY)

32
Q

Sulfonamides prevent formation of ______

A

Dihydrofolic Acid (from Dihydropterate Diphosphate and PABA)

33
Q

Trimethoprim prevents formation of ______

A

Tetrahydrofolic Acid (from Dihydrofolic Acid)

34
Q

MIC vs MBC

A

MIC: lowest concentration of antibiotic that INHIBITS growth

MBC: lowest concentration of antibiotic that KILLS 99.9%

Microbiology Exam 1 (11 decks)

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