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IAHI Block 2 > Antibiotics and antibiotic resistance Pt. 2 > Flashcards

Antibiotics and antibiotic resistance Pt. 2 Flashcards

1
Q

Vancomycin Mechanism of action

A

Binds to D-ala-D-ala at the end of peptide side chain in peptidoglycan precursors, blocking PBPs from catalzying crosslinking

Effective on many Gram-positives but not on gram-negative because vancomycin is too big to penetrate pores of outer membrane of gram-negative

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2
Q

Vancomycin mechanism of resistance

A
  • Modification of antibiotic target - altered peptidoglycan structure that lacks D-ala-D-ala groups
  • Genes encoding resistance found on plasmids or transposons transferred between bacteria
  • Vancomycic resistance often associated with enterococcie in hospital settings (VRE)
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3
Q

Cycloserine

Function:

Mechanism of Action

A

Function: Inhibits peptidoglycan crosslinking

  • Structurally similar to D-alanine
  • Used as second line anti-tuberculosis therapy

Mechanism of Action: Competitive inhibitor of D-alanine in two sequential reactions

  • Alanine racemase (L-ala to D-ala)
  • D-alanyl-D-alanine synthetase (D-ala to D-ala-D-ala)
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4
Q

Bacitracin

Use:

Mechanism of Action:

_______ are 10 times more sensitive than other related bacteria

A

Use: Bacitracin “A disks” are a diagnostic test for Group A Streptococci - too toxic for systemic use

Mechanism of action: Binds to pyrophospate on the lipid carrier for peptidoglycan precursors and blocks its recycling

Group A Streptococci

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5
Q

Daptomycin:

Mechanism of action:

A

Daptomycin: Lipopetide antibiotic; bactericidal, narrow spectrum (Gram positive)

Mechanism of action: Binds to and disrupts cytopasmic membrane, possibly via loss of membrane potential

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6
Q

Polymyxins:

Mechanism of Action:

Adverse Effects:

A

Polymyxins: Lipopeptide antibiotics - bactericidal narrow spectrum (Gram negative)

Mechanism of Action: Bind to LPS in outer membrane of gram negative bactera, leading to disruption of both the outer membrane and cytoplasmic membrane

Adverse Effects: due to toxicity, limit use to infections caused by antibiotic resistant bacteria or topical use

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7
Q

Bacterial protein synthesis (translation)

A

Protein synthesis occurs in 2 phases: intiation and elongation

30S subunit forms “initiation complex” w/ mRNA message, initiation tRNA

The 50S subunit joins, resulting in the functional 70S ribosome that forms peptide bonds to produce the protein

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8
Q

Tetracyclines

Type:

Mechanism of Action:

A

Type: Bacteriostatic, broad spectrum

Mechanism of Action: Binds to 30S ribosomal subunit and interferes with binding of aminoacyl tRNA to the ribosome

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9
Q

Mechanism of resistance to tetracycline

A
  • Tetracycline efflux pump - most common
  • Mutations on the ribosome

*Tetracycline has lost its effectiveness due to overuse and widespread resistance

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10
Q

Aminoglycosides

Type:

Mechanism of Action:

A

Type: Bactericidal, broad spectrum

Mechanism of Action: Binds irreversibly to 30S ribosomal subunit and causes misreading and premature release of ribosome from mRNA

  • Gram negatives > gram positives
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11
Q

Aminoglycosides

Adverse effects:

Mechanism of resistance:

A

Adverse effects: Ototoxic and nephrotoxic

Mechanism of resistance: Enzymatic modification of the antibiotic to prevent aminoglycoside binding to the ribosome

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12
Q

Macrolides

Type:

Mechanism of Action:

A

Type: Bacteriostatic, primarily active against Gram-positive bacteria (useful in patients allergic to β-lactams)

Mechanism of Action: Binds 50S ribosomal subunit to block elongation of proteins

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13
Q

Macrolides Mechanism of Resistance (2)

A
  1. Enzymatic modification (methylation) of ribosomal RNA - Erythromycin can’t bind methylated ribosome
  2. Efflux pumps can expel macrolides from cells enabling protein synthesis to occur
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14
Q

Chloramphenicol

Type:

Toxicity:

A

Type: Bacteriostatic

Toxicity: Potential toxicity limits use to very severe infections

Toxicity probably derives from lack of selectivity - inhibits ribosomes in mitochondria

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15
Q

Chloramphenicol

Mechanism of Action:

Mechanims of resistance:

A

Mechanism of Action: Binds 50S ribosome subunit to inhibit peptidyl transferase activity - elongation

Mechanims of resistance: Bacterial enzyme catalyzes addition of acetyl group to drug preventing ribosome binding

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16
Q

Clindamycin

Type:

Use:

A

Type: Bacteriostatic (inactive against gram-negative)

Use: Useful for treatment of community acquired MRSA (Methicillin-resistant Staphylococcus aureus); often used to treat infections by toxin-producing S. aureus

17
Q

Clindamycin

Mechanism of Action:

Mechanism of Resistance:

A

Mechanism of Action: Binds 50S ribosomal subunit

Mechanism of Resistance: Enzymatic modification (methlylation) or rRNA

Exhibits cross-resistance with macrolides (bacteria that are resistant to macrolides are also resistant to clindamycin)

18
Q

Linezolid (Status, Treatment)

A

New class of antibiotic - inhibitor of protein synthesis - first new antibiotic in > 30 years

Indicated in treatment of complicated skin infections caused by Staphylococcus aureus, Streptococcus pyogenes, or Streptococcus agalactiae (not effective against most gram-negative)

19
Q

Linezolid

Mechanism of Action:

Mechanism of resistance:

A

Mechanism of Action: Binds to unique site on 50S subunit to prevent formation of 70S complex

Mechanism of resistance: Point mutations in ribosomal components that prevent linezolid binding - no cross resistance with other antibiotics

20
Q

1st generation inhibitor of DNA replication

Mechanism of Action:

A

Nalidixic acid - synthetic quinolone

Mechanism of Action: binds bacterial DNA gyrase and or topoisomerase to inhibit its catalytic function - disrupts DNA replication and repair - results in DNA damage

21
Q

2nd generation inhibitors of DNA replication

A

Fluoroquinolones - Bactericidal, broad spectrum

Same mechanism of action as Nalidixic acid

22
Q

Inhibitors of DNA replication - Mechanisms of resistance (2)

A
  1. Point mutations in bacterial DNA gyrase prevent antibiotic binding and render the enzyme resistant to the action of quinolones
  2. Efflux pump-mediated resistance also observed
23
Q

Metronidazole

Use:

Mechanism of Action:

A

Use: Used to treat anaerobic bacterial infections; common treatment for C. difficile pseudomembranous colitis

Mechanism of Action: in an anaerobic environment a radical is produced, leading to toxic metabolites that damage DNA

24
Q

Rifampicin:

Mechanism of action:

Mechanism of resistance:

A

Mechanism of action: Binds β-subunit of bacterial RNA polymerase to inhibit RNA synthesis (rapid selection for resitance)

Mechanism of resitance: Acquisition of mutations in β-subunit of RNA polymerase that prevent antibiotic from binding

25
Q

Fidaxomicin

Mechanism of Action:

A

Bactericidal

Mechanism of Action: Noncompetitive inhibitor of RNA synthesis by binding bacterial RNA polymerase

26
Q

Anitmetabolites: Metabolic analogs as antibiotics

A

Metabolic analogs are structurally similar to natural metabolic intermediates - the analogs act as competitive inibitors to block the normal biosynthetic pathway

27
Q

Tetrahydrofolate biostynthesis pathway metabolic analogs and their mechanism of resistance

A

Sulfonamides are metabolic analogues of p-aminobenzoic acid

Trimethoprim is a metaboilc analog of dihydrofolate - inhibits dihydrofolate reductase

Mechanism of resistance: acquisition of another gene encoding dihydrofolate reductase

28
Q

Benefits of antibiotics used in combination

A
  1. Prompt treatment for undetermined life-threatening pathogen infection
  2. Mixed infection caused by bacteria with different susceptibility profiles
  3. To avoid or delay emergence of resistant mutants during long-term antibiotic therapy
  4. Synergy: the combined action of 2 drugs is greater than the sum of individual drugs
29
Q

Examples of synergy

A
  1. Two drugs act sequentially to block an essential metabolic pathway (Sulfonamides and trimethoprim)
  2. One drug enhances the uptake of another drug (Penicillins enhance uptake of aminoglycosides)
  3. One drug may prevent the inactivation of another drug (Clavulanic acid inactivates β-lactamase)
30
Q

Antagonism

A

Combing β-lactams can be antagonistic - some β-lactams strongly induce AmpC β-lactamases that can degrade many penicillins and 2nd and 3rd generation cephalosporins

31
Q

Indifference

A

2 agents don’t work any better together or worse than single agent

32
Q

Biofilms

A

Bacteria growing in a multicellular aggregate on surface - likely responsible for many chronic infections

  • Enhanced tolerance to antibiotics - partly due to non-growing state

IAHI Block 2 (12 decks)

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