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Antibiotics > Antibiotic types > Flashcards

Antibiotic types Flashcards

1
Q

Classes of antibiotics

A 
(BFMATS) 
Beta lactams 
Fluoroquinolones 
Macrolides 
Aminoglycosides 
Tetracylines 
Sulfonamides
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2
Q

Beta Lactams

A 
Inhibit cell wall synthesis (bacteriocidal) 
4 types: 
- Penicillins 
- Cephalosporins 
- Carbapenems 
- Monobactams

Eg. Penilcilin G, Amoxicilin, Flucoxacilin

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3
Q

Fluoroquinolones

A

Inhibit DNA synthesis (bacteriocidal)

Eg. Norflaxacin
Ciproflaxacin

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4
Q

Macrolides

A

Inhibit protein synthesis, target 50S subunit (bacteriostatic)

Eg. Erythromycin

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5
Q

Aminoglycosides

A

Inhibit protein synthesis
target 30S subunit

Eg. gentamicin, streptomycin

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6
Q

Tetracylines

A

Inhibit protein synthesis

target the 30S subunit

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7
Q

Sulfonamides

A

Block bacterial cell metabolism by inhibiting enzymes

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8
Q

Beta lactams mechanism

A
  • Gram positive and gram negative bacteria have peptidoglycan
  • The peptidoglycan layer is made from alternating NAG (N-acetyl glucosamine) and NAM (N-acetyl muramic acid) and amino acid cross links
  • The transpeptidase enzyme (penicillin binding protein) is involved in cross linking
  • B- lactams contain a B-lactam ring that is able to bind to the enzymes that cross link peptidoglycans
  • They interfere by binding to transpeptidase, preventing bacterial cell wall synthesis
  • Gram positive bacteria have a high internal osmotic pressure, without a firm cell wall they burst
  • The antibiotic + penicillin binding protein complex stimulate the release of autolysins that are able to digest the existing cell wall
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9
Q

B- lactam resistance

A
  • Enzymatic inactivation
  • Bacteria synthesise a B-lactamase, an enzyme that attacks the B-lactam ring
  • It is most commonly produced by gram negative bacteria
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10
Q

Macrolide resistance

A
  • Post transcriptional mutation of the 23S rRNA
  • Drug inactivating esterases
  • Efflux pumps
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11
Q

Tetracyline resistance

A
  • Enzymatic inactivation of tetracyline
  • Efflux pumps (encoded on plasmid)
  • Stop protein binding to tetracyline
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12
Q

Fluoroquinolone resistance

A
  • Produce proteins that bind to DNA gyrase, protecting it from quinolones
  • Efflux pumps
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13
Q

Aminoglycoside resistance

A
  • Decreased cell permeability
  • Altering ribosomal binding site
  • Aminoglycoside modifying enzyme
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14
Q

Antibiotics that inhibit cell wall synthesis

A
  • Beta lactams
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15
Q

Antibiotics that inhibit nucleic acid synthesis

A

Inhibit DNA gyrase/ toiposomerase IV: quinolones

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16
Q

Antibiotics that inhibit protein synthesis

A

Inhibit 50S subunit:
- macrolides

Inhibit 30S subunit:

  • aminoglycosides
  • tetracylines
17
Q

Mechanism of antibiotic resistance

A

PEDA

  • Pumps (efflux)
  • Enzymatic inactivation
  • Decreased permeability
  • Altered target site
18
Q

Why are some penicillins not effective against gram negative bacteria

A
  • Penicilins act on the peptidoglycan layer
  • Gram negative bacteria have a thin peptidoglycan layer
  • They have a second cell membrane outside the peptidoglycan layer so it’s harder for the penicillin to reach
19
Q

How are resistant genes carried in bacteria

A

On the plasmid

20
Q

Antibiotic resistance

1. Efflux pumps

A

Present in both gram +ve and gram -ve bacteria, on the inner membrane
Active transporters

They are classified based on their amino acid sequence:
All are present in gram +ve and gram -ve bacteria except the RND family
- The major facilitator superfamily (MFS)
- ATP binding cassette superfamily (ABC)
- Small multi drug resistant family (SMR)
- Resistance nodulation cell division superfamily (RND), gram -ve bacteria
- The multi antimicrobial extrusion protein family (MATE)

Efflux pumps are multifunctional tools. In E.coli they are responsible for the secretion of hemolysin which is a toxin

21
Q

Antibiotic resistance

2. Enzymatic inactivation

A

Eg. Beta lactamases

They inactivate the B-lactam ring so the B-lactam can’t bind to the transpeptidase

22
Q

Antibiotic resistance

3. Decreased permeability

A

By decreasing permability of the drugs across the cell surface

23
Q

Antibiotic resistance

4. Altered target site

A

Change the structure of the protein
Eg. Modifying the penicillin binding protein (peptidase) so that antibiotics can no longer bind to the PBP and prevent its action. In MRSA, bacteria are resistant to methicillin because the protein that methicillin bind to is modified in the bacteria

Another protective mechanism found among bacteria is ribosomal protection proteins. These proteins protect the bacterial cell from antibiotics that target the cell’s ribosome to inhibit protein synthesis. This mechanism involves the binding of ribosomal protection proteins to the ribosomes of the bacterial cell, which changes its conformational shape. This allows the ribosomes to continue synthesizing proteins essential to the cell while preventing antibiotics from binding to the ribosome to inhibit protein synthesis

24
Q

Antibiotic resistance

Modifying the drug by enzymes

A

Eg. Streptomycin can be inactivated by:
- Phosphorylation
The gene that confers resistance: APH
- Chromosomally acquired streptomycin resistance is due to mutations encoding for the ribosomal protein S12, rpsl (altered target site)

Eg. Chloramphenicol: protein synthesis inhibitor, target the 50S subunit

  • Modify the drug by acetylation
  • Chromosomally encoded cmlA produces more OmpA leading to reduced permeability of the bacterial cell membrane
25
Q

General antibiotic resistance

A

A lot of antibiotics modes of action require getting into the cell (protein synthesis inhibitor)
Bacteria upregulate genes that produce proteins that alter the membrane permeability
It is a problem when you target something that is essential to bacteria

26
Q

Antibiotic resistance genes

A

Present on:

  • Chromosomes
  • Plasmids

Transferred:

  • Vertical transmission
  • Horizontal transmission
27
Q

Mechanisms of horizontal gene transfer

A

Transformation, mediated by competence proteins. The DNA is taken up from the environment
Transduction, the use of bacteriophage. Inject DNA into a cell
Conjugation, a mechanism of transferring resistant genes from one bacteria to another

Antibiotics (10 decks)

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