Infection - Antimicrobials Flashcards

1
Q

What is the difference between a bactericidal and a bacteriostatic agent?

A

Bactericidal kills the bacteria, while bacteriostatic inhibits the growth of an organism

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2
Q

What is the strict definition of an antibiotic?

A

A type of antimicrobial drug derived from another living creature, eg. fungi

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3
Q

What is the basis of an ‘antibacterial class’?

A

They are sorted by chemical structure

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4
Q

Give some ideal features of antimicrobial agents

A
  • selectively toxic
  • few adverse effects on host
  • reaches site of infection
  • oral/IV formulation
  • long half-life to allow infrequent dosing
  • no interference with other drugs
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5
Q

What are the four main ways that antibacterials work on bacteria?

A

They interfere with:

1) cell wall synthesis
2) protein synthesis (tetracyclines, aminoglycosides, macrolides)
3) cell membrane function (polymixins)
4) nucleic acid synthesis (quinolones)

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6
Q

How does penicillin affect the bacterial cell wall?

A

Cell wall is composed of cross-linked chains of peptidoglycans which are joined by penicillin bonding protein.

Penicillin binds to the protein, preventing it from joining the chains together and destabilising the wall.

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7
Q

How does vancomycin disrupt the bacterial cell wall?

A

It binds to the end of the links between the chains, meaning that they cannot bind to penicillin binding protein and they are not joined

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8
Q

How do fluoroquinolones interfere with protein synthesis?

A

They inhibit enzymes involved with DNA replication, one of which is responsible for supercoiling the DNA

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9
Q

What are the three types of antibiotic resistance?

A
  • INTRINSIC (no target/access for the drug, usually permanent)
  • ACQUIRED (acquires new genetic material/mutates, usually permanent)
  • ADAPTIVE (organism responds to a stress, usually reversible)
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10
Q

Give some mechanisms of antibiotic resistance

A
  • bacteria may produce enzyme which inhibits the drug, eg. beta-lactamases
  • target enzyme has lowered affinity for antibacterial agent
  • may be altered uptake of drug (eg. decrease in permeability of cell wall or increased efflux)
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11
Q

How does chromosomal gene mutation lead to an antibiotic resistant strain of bacteria developing?

A
  • mutated gene confers resistance in one bacterium
  • other bacteria are killed by antibiotics
  • the resistant strain multiplies and becomes dominant
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12
Q

How can the gene for antibiotic resistance move directly from one bacterium to another?

A

Horizontal gene transfer - plasmid moves from one bacterium to another via a pilus

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13
Q

How does disc sensitivity testing measure antibiotic activity?

A

Filter paper disc is impregnated with antibiotic and placed on a petri dish which has been covered with a sample of bacteria. It is incubated to see whether the organism grows or not. How much/little it grows = how well the antibiotic works

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14
Q

What is the ‘minimum inhibitory concentration’?

A

The lowest concentration at which the antibiotic still kills bacteria in a solution

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15
Q

What are beta-lactams?

A

A class of broad-spectrum antibiotics consisting of all antibiotic agents that contain a beta-lactam ring in their molecular structures. Group includes penicillins, cephalosporins, carbapenems and monobactams

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16
Q

Give some examples of penicillins and what they work against

A
  • penicillin (streptococci mainly)
  • amoxicillin (streptococci and gram-negatives)
  • flucloxacillin (staphlococci and streptococci)
  • co-amoxiclav and piperacillin (all of the above and gram negative)
17
Q

Give two examples of drug classes that are very broad spectrum and work against most gram negatives

A

Cephalosporins and carbapenems (there are other answers too)

18
Q

Do glycopeptides work better against gram positive or gram negative?

A

Active against most gram positive

19
Q

Why are tetracyclines sometimes given in the place of another drug?

A

In penicillin allergy, they are given instead of penicillin

20
Q

Why shouldn’t tetracyclines be given to children younger than 12 years old?

A

They stain teeth and bone yellow

21
Q

What situation are aminoglycosides usually reserved for?

A

Severe gram negative sepsis

22
Q

Give some examples of macrolides

A

Erythromycin and clarithromycin

23
Q

What are macrolides active against?

A

Atypical respiratory pathogens and mild gram positive infections

24
Q

How do quinolones work?

A

They inhibit DNA gyrase

25
Q

What is trimethoprim often used to treat?

A

UTIs

26
Q

How does trimethoprim and sulphonamides work?

A

They inhibit folic acid synthesis

27
Q

Give some examples of antifungals

A
  • azoles (active against yeasts and molds, inhibit cell membrane synthesis)
  • polyenes (inhibit cell membrane function)
28
Q

What is metronidazole?

A

An antibacterial and antiprotozoal agent which works against anaerobic bacteria and certain protozoa