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Block 1 - Week 4 > Introduction to antibiotics > Flashcards

Introduction to antibiotics Flashcards

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1
Q

What is a key feature of the Beta-Lactam antibiotic structure?

A

The beta-lactam ring

This ring has to be intact in order for the drug to be active

Also has thiazolidine ring

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2
Q

How do beta-lactam antibiotics kill bacteria?

A
  • As D-Ala-D-Ala analogs, they covalently bind to specific receptors (penicillin-binding proteins, aka PBPs)
  • Act as competitive inhibitor to transpeptidase
  • Also activate autolysins (bacterial enzymes that remodel/breadk down cell wall) –> Causes lesions in cell membrane and wall
  • Thus inhibiting bacterial cell wall synthesis
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3
Q

What are the three main mechanisms microbes develop antibiotic resistance?

A
  1. ) Production of drug-inactivating enzymes
  2. ) Change structure of receptor or binding site (decrease affinity for the drug)
  3. ) Changes in drug permeation and transport (decreasing drug accumulation)
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4
Q

Bactericidal agents

A

Kills the bacteria

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5
Q

Bacteriostatic agents

A

Stop bacteria from reproducing while not necessarily killing them

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6
Q

Why can bacterial cells survive in water?

A

The bacterial cell wall prevents lysis from high osmotic pressure. If a human cell was placed in water the osmotic pressure would cause it to lyse.

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7
Q

Porin

A

Channels on proteins that are permeable to hydrophilic substances such as B-Lactams

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8
Q

What is peptidoglycan polymer chain?

A

The basic unit of the cell wall

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9
Q

What does the peptidoglycan polymer chain consist of?

A

Polysaccharides with alternating aminohexoses:

  • N-acetylmuramic acid
  • N-acetylglucosamine
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10
Q

What does the peptidoglycan polymer chain terminate in?

What is the relevance of this?

A

D-Alanine-D-Alanine + pentaglycine bridges

This is where cross-linking occurs, and B-lactams are structural analogs of the D-Ala-D-Ala substrate and therefore acts as competitive inhibitor

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11
Q

Transpeptidation in bacterial cell wall formation

A

A transpeptidase enzyme links the pentaglycine bridge of one peptidoglycan to the D-Ala-D-Ala of another forming the cross-link

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12
Q

What mechanisms can make a bacteria resistant to penicillin?

A
  1. ) Inactivation via plasmid-mediated B-lactamase (penicillinases) –> Most staphylococci and many gram (-) organisms
  2. ) Modification of PBPs to decrease affinity for drug –> MRSA, MRSE, and PRSP
  3. ) Impaired penetration to target PBPs (changes in porin structure in gram (-) rods)
  4. ) Presence of efflux pump
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13
Q

Cephalosporin main structure

A

B-lactam ring

Dihydrothiazine ring

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14
Q

Cephalosporin class

A

Class of B-lactam antibiotics

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15
Q

Cephalosporin mechanism of action

A
  • Very similar to penicillin
  • D-Ala-D-Ala analogs, bind to PBP, inhibit transpeptidase
  • Activate autolysins
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16
Q

Monobactams

A
  • Has monocyclic B-lactam ring (B-lactam class of Abxs)
  • Drug name: Aztreonam
  • Binds to a specific PBP (PBP3)
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17
Q

Carbapenems

A
  • Synthetic B-lactam drugs structrually related to penicillins (B-lactam ring + 5-membered penem ring)
  • Common drugs: Imipenem, Meropenem, Doripenem, and Ertapenem
  • Resistant to most B-lactamases, but susceptible to metallo-B-Lactamase
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18
Q

B-lactamase inhibitors (basics)

A
  • Resemble B-lactam drugs
  • Inhibit B-lactamases by competitive inhibition
  • Have low antibiotic activity when used alone
  • Used with penicillins in fixed combinations
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19
Q

What are the main B-lactamase inhibitor/penicillin combinations?

A
  • Timentin: Ticarcillin + Clavulanic acid
  • Augmentin: Amoxicillin + Clavulanic acid
  • Unasyn: Ampicillin + Sulbactam
  • Zosyn: Piperacillin + Tazobactam
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20
Q

What class of antibiotics do penicillins and cephalosporins belong to?

A

B-Lactams

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21
Q

What penicillin drug and B-lactam inhibitor make up Augmentin?

A

Amoxicillin + Clavulanic acid

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22
Q

What penicillin drug and B-lactam inhibitor make up Unasyn?

A

Ampicillin + Sulbactam

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23
Q

What penicillin drug and B-lactam inhibitor make up Zosyn?

A

Piperacillin + Tazobactam

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24
Q

What penicillin drug and B-lactam inhibitor make up Timentin?

A

Ticarcillin + Clavulanic acid

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25
Vancomycin
- No B-lactam ring (doesn't bind to PBPs) - NOT susceptible to B-lactamases - Binds firmly to D-Ala-D-Ala terminus of peptidoglycan pentapeptide, thereby blocking the Transglycosylase Enzyme, thus blocking peptidoglycan elongation and cross-linking - Also damages cytoplasmic membranes
26
Penicillin-Binding-Proteins (PBPs)
- Involved in final stages of peptidoglycan synthesis - Are the target of beta-lactam antibiotics - Belong to a group of enzymes called transpeptidases
27
What is the mechanism of Vancomycin resistance?
- Terminal D-Ala is replaced by D-lactate --> Decreases affinity of vancomycin - Plasmid-mediated changes in permeability to the drug
28
What are come common Vancomycin-resistant bacteria?
- VRE: Vancomycin-resistant enterococci | - VRSA: Vancomycin-resistant staphylococcus aureus
29
Daptomycin
- Structure: novel cyclic lipopetide with spectrum similar to vancomycin - Disrupts multiple aspects of bacterial cell membrane (creates holes that leak ions, causing depolarization)
30
Fosfomycin
- Antimetabolite inhibitor of cytosolic enolpyruvate transferase --> prevents the formation of N-acetylmuramic acid (precursor of peptidoglycan chain)
31
Cycloserine
An antimetabolite that blocks the incorporation of D-Ala into the pentapeptide side chain of the peptidoglycan
32
Bacitracin
A peptide antibiotic that interferes with a late stage in cell wall synthesis in gram (+) organisms
33
What is the mechanism of action of Ribosomal Antibiotics?
Inhibit protein synthesis by binding to and interfering with ribosomes
34
List of Ribosomal antibiotics
- Spectinomycin - Macrolides - Aminoglycosides - Lincosamides - Linezolid - Chloramphenicol - Tetracyclines - Streptogramins
35
Bacterial ribosomes
- 70S --> 30S + 50S subunits - Free in the cytoplasm - Bind to mRNA - Form polysomes (cluster of ribosomes held together by a strand of mRNA that each ribosome is translating) - Display receptors for antibiotics on either subunit
36
Eukaryotic ribosomes structure and relevance to antibiotics
80S --> 40S + 60S subunits Allows for antibiotics to be selective for bacterial ribosomes and not eukaryotic ribosomes; however, due to the simularities, ribosomal antibiotics have some degree of toxicitiy
37
Bacterial protein synthesis main steps
1. ) Initiation (binds mRNA) 2. ) Aminoacyl-tRNA binding (delivers AA) 3. ) Transpeptidation by peptidyl transferase (growing peptide and new AA combined) 4. ) Translocation (ribsome slides over on mRNA to next codon)
38
Which ribosomal antibiotics effect the 30S subunit? What step of translation do they effect?
- Spectinomycin - Aminoglycaosides - Tetracyclines I SAT on the small subunit
39
What ribosomal antibiotics effect the 50S subunit? What step of translation do they each effect?
All of the ones that don't effect the 30S - Chloramphenicol - Macrolides - Lincosamides - Streptogramins - Linezolid
40
Spectinomycin - Structure - Bactericidal or Bacteriostatic? - Which subunit does it bind? - Mechanism of action?
- Aminocyclitol that is structurallly related to aminoglycosides - Bacteriostatic - Binds 30S subunit - Inhibits formation of 70S initiation complex
41
Mechanism of Spectinomycin resistance
- Production of drug inactivating enzyme | - Alteration of specific receptor on 30S subunit
42
Aminoglycosides examples
- Neomycin - Gentamicin - Streptomycin
43
Aminoglycosides mechanism of action
- Binds to 30S subunit - Blocks formation of 70S initiation complex - Causes misreading of mRNA - Prevent polysome formation, resulting in nonfunctional monosome - Irreversibly inhibits protein synthesis --> bactericidal
44
Aminoglycosides mechanisms of resistance
- Produce (plasmid-mediated) drug-inactivating group transferases --> includes: - Aminoglycoside acetyltransferase - Aminoglycoside adenyltransferase - Aminoglycoside phosphotransferase - Alter 30S subunit (lowers affinity for Abx) - Alter permeability
45
Tetracyclines mechanism of action
- Bind 30S subunit - Inhibit binding of aminoacyl-tRNA to mRNA-ribosomal complex - Bacteriostatic
46
Tetracycline mechanism of drug resistance
- Efflux of drugs by plasmid-coded efflux protein pump (Unique to Tetracyclines!) - Altered permeability to drug - Enzymatic inactivation of the drug
47
Chloramphenicol mechanism of action
- Binds 50S subunit - Bacteriostatic - Inhibits Peptidyl Transferase (in transpeptidation)
48
Chloramphenicol mechanism of drug resistance
- Produce (plasmid-coded) drug inactivating enzyme: Chloramphenicol Acetyltransferase - Reduce permeability
49
Macrolides example
Erythromycin
50
Macrolides mechanism of action
- Bind 50S subunit - Bacteriostatic - Prevent the ribosome from translocation down the mRNA
51
Macrolides mechanism of drug resistance
- Methlyation of the receptor on the 50S subunit (plasmid-coded methylase) results in decreased affinity for the Abx - Drug inactivating enzymes (esterases that hydrolyze macrolides) - Reduced permeability to the drug
52
Lincosamides examples
- Lincomycin | - Clindamycin
53
Lincosamides mechanism of action
- Binds 50S subunit - Prevent the ribosome from translocating down the mRNA - Bacteriostatic
54
Lincosamide mechanism of drug resistance
- Methlation of the ribosomal receptor site - Production of drug inactivating enzymes - Reduced permeability to the drug
55
Streptogramins mechanism of action
- Binds to different sites on 50S ribosomal subunit - Works syndergistically to prevent the ribosome from translocating down the mRNA - For most susceptible organisms, they are bactericidal
56
Streptogramins mechanism of drug resistance
- Methylation of the quinupristin (S-type B) binding site - Production of drug inactivating enzyme - Active transport efflux
57
Streptogramins example
Synercid --> Composed of Streptogramins B & A (also known as quinupristin and dalfopristin)
58
MLS-type B resistance
- Macrolide-Lincosamide-Streptogramin-B resistance | - Methylase production confers resistance to the above antibiotics as they have the same ribosomal binding site
59
Linezolid mechanism of action
- Binds to unique site located on 23S rRNA of the 50S subunit - Inhibit the formation of 70S ribosome (initiation complex) - Also inhibits translocation of peptidyl-tRNA
60
Linezolid mechanism of drug resistance
- Mutation of the binding site on 23S rRNA (decreases affinity for Abx)
61
Sulfonamides and Trimethoprim drug class
Antifolate drugs (often used in combination with eachother)
62
Sulfonamides mechanism of action
- As antimetabolites of PABA (para-aminobenzoid acid) they are competitive inhibitors of DHPS (dihydrop'teroate synthase) in bacteria (competing with the PABA precursor)
63
Sulfonamides mechanism of resistance
- Decrease intracellular accumulation - Increase in production of PABA - Decrease in sensitivity of DHPS to the drugs
64
Trimethoprim mechanism of action
Act as a selective inhibitor of DHFR (dihydrofolate reductase)
65
Trimethoprim mechanism of resistance
Decrease in the sensitivity of DHFR to the Abx
66
Fluoroquinolones mechanism of action
- Inhibit prokaryotic topisomerase II (DNA Gyrase) and topiosomerase IV - Bactericidal
67
Fluoroquinolones mechanism of resistance
- Decrease in intracellular accumulation (efflux pump or change in porin structure) - Chromsome-encoded mutation in DNA gryase - Plasmid-mediated resistance
68
Penicillins, Cephalosporins, Monobactams, and Carbapenems general mechanism of action
- Bind to PBPs as Ala-AAla analogs - Inhibit transpeptidase - Inhibit cross-linking of peptidoglycan polymers - Activate autolysins
69
Penicillin, main mechanisms of resistance
- B-lactamases | - Modification of PBPs (Ex. MRSA/E and PRSP)

Block 1 - Week 4 (11 decks)

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