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Pathology > Antibiotics > Flashcards

Antibiotics Flashcards

1
Q

Antimicrobial

A

Interferes with growth and reproduction of a microbe

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2
Q

Bactericidal

A

Kills bacteria

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3
Q

Bacteriostatic

A

Halts bacterial growth, but does not kill bacteria

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4
Q

What is the most essential component to efficacy of an antibiotic?

A

Selective toxicity (bacteria harmed but not the host)

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5
Q

The bacteria structure targeted must be..

A

Not present in host

Different to that in the host

Or with differential access in host and bacterium

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6
Q

The four main antibiotic targets are…

A

Cell wall, nucleic acids, ribosomes and cell membranes

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7
Q

Wide spectrum vs narrow spectrum antibiotics

A

Wide spectrum - target many different bacterial types

Narrow spectrum target one individual type

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8
Q

What two types inhibit cell wall synthesis?

A

Beta-lactams

Glycopeptides

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9
Q

Beta lactam examples

A

Penicillin, amoxicillin

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10
Q

Beta lactam function

A

Block peptide cross-linking in growing cell wall, prevent PG synthesis

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11
Q

Target of beta-lactams (penicillin)

A

Target penicillin binding proteins, which are required for proteoglycan synthesis

Transpeptidase are penicillin binding proteins which are targets of Beta lactam antibiotics.

Similar in structure to D-alanyl-D-alanine peptide of proteoglycan cross link, so binds in active site for transpeptidase enzyme - preventing final cross-linking step.

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12
Q

Beta lactam resistance

A

Resistance results from bacteria using D-lactate instead of alanine in PG

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13
Q

Is beta lactam bactericidal or bacteriostatic?

A

Bactericidal but kills cells only when they are growing. For example, no growth, no cross linking needs to occur.

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14
Q

Glycopeptide example

A

Vancomycin

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15
Q

Role of glycopeptide antibiotics

A

Large hydrophilic molecule, forms hydrogen bonds with terminal D-alanyl-D-alanine, peptide of proteoglycan cross links.

Targets PG itself so only active on gram positive bacteria.

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16
Q

Is glycopeptide bactericidal or bacteriostatic?

A

Bacteriostatic

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17
Q

3 bacterial protein synthesis (ribosome) inhibiting antibiotics (and examples)

A

Macrolides (erythromycin)
Aminoglycosides (gentamicin, tetracycline, streptomycin)
Chloramphenicol

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18
Q

Macrolide action

A

Inhibit transcription by binding to 50s subunit and prevent escape of tRNA once it has donated its amino acid. Thus, new tRNA cannot attach.

Bacteriostatic

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19
Q

Aminoglycoside action

A

Inhibition of the initiation complex and of messenger RNA.

No translation and no protein production

Bacteriostatic

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20
Q

Chloramphenicol action

A

Inhibits peptidyl transferase, preventing synthesis of new peptide bonds, selectively bacteria as binds to 50s subunit not human 60s.

Bacteriostatic

21
Q

Why are ribosomes an appropriate antibiotic target?

A

Ribosomes are a key target as very different sizes in eukaryotes and prokaryotes.

Bacteria (30s and 50s unit), humans (60s and 40s unit).

22
Q

Inhibitor of transcription antibiotic example

A

Rifamycin (rifampicin)

23
Q

Rifamycin action

A

Inhibitors of (m)RNA synthesis, by affecting bacterial RNA polymerase without affecting RNA pol of human cells.

Anti-tuberculosis

Bactericidal

24
Q

What antibiotic inhibits folate metabolism (and DNA synthesis?

A

2,4-diaminopyridines (i.e trimethoprim)

25
Q

What antibiotics inhibit DNA synthesis by binding DNA gyrase?

A

Quinolones, fluoroquinolones (i.e ciprofloxacin)

Inhibits DNA gyrase (topoisomerase in prokaryotes)

UTIs, lower respiratory tract infections

Bactericidal

26
Q

What is DNA gyrase?

A

Prokaryote topoisomerase (DNA uncoiler)

27
Q

Role of sulphonamides

A

Antifolates, block the synthesis of tetrahydrofolic acid, which is required in the synthesis of nucleic acids.

Sulphonamide compete with PABA in active site of dihydropteroate synthetase (important enzyme in synthesis of THFA).

28
Q

When would one combine antibiotics?

A

Empiric therapy with broad spectrum antibiotics is important when the agent is unknown.

Can give complimentary, synergistic action to stamp out an infection

Combination of bactericidal and bacteriostatic is important for killing a population

Likely to reduce emergence of resistance as a wider range of bacteria can be killed

29
Q

When and why would one use specific therapy?

A

Transition to a specific therapy when identification has been done - reduces resistance risk (less bacteria species are put under a selection pressure).

30
Q

What is the MIC, why is it important?

A

Minimum inhibitory concentration, antibiotic must remain above this at all times

31
Q

Target site insensitivity resistance

A

Changes to ribosome structure in erythromycin resistance.

Erythromycin can no longer bind and inactivate the ribosome

32
Q

Enzymatic inactivation resistance

A

Beta-lactamases in penicillin resistance: Beta-lactamases are enzymes produced by bacteria that provide multi- resistance to β-lactam antibiotics such as penicillin.

Beta-lactamase provides antibiotic resistance by breaking the antibiotics’ β-lactam ring open, deactivating the molecule’s antibacterial properties.

Beta lactamase inhibitors provide a therapeutic option to combat resistance.

33
Q

Cell wall impermeability resistance

A

Mutant porins in G-bacteria

34
Q

Drug export resistance

A

Gyrase mutations in quinolone resistance

35
Q

Increased efflux resistance

A

Through the presence of tetracycline membrane pumps

36
Q

Target modification resistance

A

Quinolones, penicillins, change of receptor

37
Q

Target amplification resistance

A

Sulphonamides, where causes many copies of enzyme to be produced, leading to competitive inhibition.

38
Q

MRSA resistance

A

MRSA - Mec genetic element encodes a different PBP i.e. altered target site

Therefore, active site does not bind methicillin or other beta-lactam antibiotics.

Therefore, the PBP can continue to catalyse the transpeptidation reaction required for peptidoglycan cross-linking, enabling cell wall synthesis in the presence of antibiotics.

39
Q

Integrons

A

Genetic mechanisms that allow bacteria to adapt and evolve rapidly through the acquisition, stockpiling and differential expression of new genes

Genes are embedded in a gene cassette, which carries one promoterless ORF together with a recombination site

40
Q

Plasmids

A

Transferrable between strains

Many copies

Move by transformation or conjugation

41
Q

Biofilms

A

Collective of one or more types of microorganisms that can grow on many different surfaces.

Infections associated with the biofilm growth usually are challenging to eradicate.

This is mostly due to the fact that mature biofilms display antimicrobial tolerance, and immune response evasions.

Contains a supportive glycocalyx where bacteria can grow resistant to antibiotic drug.

42
Q

Overuse of antibiotics

A

Antimicrobial resistance is mainly caused by the overuse of antimicrobials.

This leads to microbes either developing a defence against drugs used to treat them, or certain strains of microbes that have a natural resistance to antimicrobials becoming much more prevalent than the ones that are easily defeated with medication

43
Q

Which of the following antibiotics acts by inhibiting bacterial transcription?

A

Rifampicin

44
Q 
Which of the following antibiotics is an example of the macrolide class of antibiotics that inhibits bacterial
protein synthesis by binding to the bacterial ribosome?
A

Erythromycin

45
Q

Which of the following antibiotics inhibits the bacterial enzyme DNA gyrase, leading to disruption of bacterial
DNA synthesis?

A

Ciprofloxacin

46
Q

What class of antibiotic is penicillin?

A

A beta lactam

47
Q

What is the bacterial enzyme inhibited by penicillin?

A

Transpeptidase

48
Q

Antibiotic that inhibits protein synthesis by blocking binding of tRNA to 30S

A

Tetracycline

Pathology (21 decks)

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