MIIM - Antibiotics I - Week 9 Flashcards

1
Q

What is the multiplication threshold for disease and what effect do antibiotics have?

A

It is the level of microbial multiplication within the body required to cause disease. It usually begins in the later phase of being infected. Antibiotics reduces microbial multiplication to be below the threshold so the disease never occurs (or much less severe symptoms)

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2
Q

What are antibiotics (and other drug classes like them) directed at?

A

Replicating organisms

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3
Q

List the four classifications of antibiotics.

A

Source
Chemical structure
Spectrum
Mechanism of action

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4
Q

Name two antibiotics classes that are classified by having a B-lactam ring.

A

Penicillin
Cephalosporin

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5
Q

Name and describe the three key considerations for an antibiotic to be safe and effective in humans (6).

A

Selective toxicity
-target the organism not humans

Access to the site of infection
-achieve adequate levels where the organism is

Provision of appropriate levels for an appropriate time
-maintain adequate levels to allow inhibition or killing

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6
Q

True or false
Organisms that are resistant to an antibiotic at one site in the body may not be resistant at other sites.

A

True - organisms resistant at one site may be sensitive at other sites

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7
Q

List 9 major sites of action that a given antibiotic can have.

A

Nucleic acid replication
Folic acid
RNA synthesis
Peptide synthesis
Nucleotide synthesis
Mycolic acid synthesis
Nicotinamide (antimycobacterial)
Cell membrane synthesis
Peptidoglycan synthesis

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8
Q

Describe how antimicrobial agents enter gram positive and negative bacteria.

A

Positive - enter easily through the loose outer wall
Negative - must go through narrow porin channels

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9
Q

Briefly describe bacterial cell wall synthesis in 5 steps.

A

Production of the peptidoglycan monomer in the cytoplasm
Transport across the membrane
Cleavage of the existing peptidoglycan by autolysins
Addition of the new monomer
Peptide crosslinking by transpeptidation by transpeptidases

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10
Q

What is the mechanism of action for a B-lactam antibiotic? What is it a structural analogue of exactly?

A

It acts as a structural analogue of D-ala - D-ala. They inhibit transpeptidases as well as enzymes that remodel the cell wall.

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11
Q

What are penicillin binding proteins and how do they determine the spectrum a given antibiotic?

A

Transpeptidases and other enzymes involved in remodelling the cell wall.
Different bacteria may have different kinds of these proteins and will therefore determine the spectrum of the antibiotic

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12
Q

Describe the consequence of an antibiotic binding to terminal D-ala - D-ala residues. Give an example of an antibiotic that does this.

A

Prevents cross-linking and thus prevents the incorporation of additional NAG-NAM subunits into the growing peptidoglycan chain, weakening the cell wall.
Vancomycin

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13
Q

Briefly describe how bacitracin antibiotics work.

A

It acts after the NAG-NAM subunit has been added to the chain.
It prevents dephosphrylation of the phospholipid carrier, preventing its regeneration.

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14
Q

What gram type is bacitracin effective against? Considering its mechanism of action, is it significantly toxic to humans or not?

A

Effective against gram positives and some gram negatives.
Has significant toxicity, so is topical only.

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15
Q

What is the consequence of inhibiting cell wall synthesis?

A

The bacteria continue to grow, the cell wall weakens, and eventually the bacteria lyses.

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16
Q

Define a spheroplast and where these can be found.

A

They are a bacterium bound by its cell membrane and lacking a cell wall. They can be found if bacteria grow in a medium in which cell wall synthesis inhibitors are found.

17
Q

Briefly describe how the cytoplasmic membrane of bacteria can be targetted. What kind of molecules do they act as? What do they interact with and what happens as a result? Are they effective against gram negative bacteria?

A

The membrane can be targetted by altering its permeability and causing leakage of intracellular components.
They act as cationic detergents.
They are effective against gram negatives.

18
Q

Consider an antibiotic that targets the cytoplasmic membrane. Would they have high or low toxicity?

A

High toxicity so topical only.

19
Q

Briefly describe the three steps of polypeptide synthesis.

A

Initiation - mRNA associates with the initiating tRNA on 30S. 50S then binds to the 30S.
Elongation - tRNA sequentially elongate the peptide chain as the mRNA moves through the ribosome.
Termination - occurs when a stop codon is reached.

20
Q

Name four stages of polypeptide synthesis that can be targetted by antibiotics.

A

Initiation
Peptidyl transfer
Translocation
tRNA synthesis

21
Q

What is the mechanism of action for aminoglycosides (2)?

A

Inhibits the initiation process by inhibiting the association of mRNA to 30S. This results in the misreading of the mRNA code.

22
Q

Which gram types are aminoglycosides effective against?

A

Gram negative and positive
(other less toxic antibiotics are more suitable for positive however).

23
Q

Do aminoglycosides have high or low toxicity?

A

High

24
Q

What are aminoglycosides reserved for?

A

Serious infections

25
Q

What do tetracyclines bind to and what happens as a result? Are tetracyclines bactericidal or bacteriostatic?

A

It bins to 30S and prevents tRNA alignment.
Generally bacteriostatic.

26
Q

Do tetracyclines have high or low toxicity?

A

Low toxicity

27
Q

Are tetracyclines rarely or widely used? What is a consequence of this?

A

Widely used to resistance is a problem.

28
Q

Briefly describe how chloramphenicol works.

A

Binds to peptidyl transferase, blocking chain elongation.

29
Q

Is chloramphenicol bactericidal or bacteriostatic?

A

Bacteriostatic

30
Q

Does chloramphenicol have high or low toxicity?

A

High

31
Q

What condition can chloramphenicol cause? Is it reversible?

A

Aplastic anaemia - irreversible

32
Q

Does chloramphenicol have a broad or narrow spectrum? Is it highly effective or not?

A

Broad spectrum, highly effective

33
Q

Briefly describe how macrolides work.

A

They bind to 50S, preventing translocation.

34
Q

Are macrolides broad or narrow spectrum?

A

Broad