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Infection. > S4L1 - Antibiotics And Resistance > Flashcards

S4L1 - Antibiotics And Resistance Flashcards

1
Q

What are the 4 main classes of antimicrobials?

A

Antibacterial, antifungal, antiviral and antiprotozoal agents

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2
Q

What is the difference between bactericidal and bacteriostatic?

A

Bacteriocidal = capable of killing bacteria

Bacteriostatic = arrest bacteria growth and multiplication.

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3
Q

What are the 4 different mechanisms of action of antibiotics?

A

Disrupting cell wall synthesis
Disrupting cell membrane function
Inhibiting nuclei acid synthesis
Disrupting protein synthesis

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4
Q

What is the difference between broad and narrow antibiotics? What are their advantages?

A

Broad spectrum = affect both gram positive and gram negative. Have more side affects as affect non-target microorganisms that may cause side affects.

Narrow spectrum = act against a small spectrum of microorganisms. Are specific to certain bacterium, will not affect many bacterium.

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5
Q

What factors need to be considered when choosing an antiobiotic?

A 
Activity against target organisms
Appropriate mode of transmission to reach site of infection 
Correct formulation (IV/Oral)
Dosing frequency/half life
Interaction with other drugs
Toxicity issues
Therapeutic drug monitoring requirements
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6
Q

What 3 mechanisms are used to measure antibiotic activity?

A

Disc diffusion testing
Broth microdilution
Strip E test

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7
Q

How does disc diffusion testing work?

A

sample is spread evenly over agar plate. Paper discs are impregnated with different antibiotics and places on the agar. Incubated over night. Measure zone of clearance to see which antimicrobial is most effective. The further the effective the more effective.

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8
Q

What is MIC?

A

The MIC is the minimum inhibitory concentration. It is the first concentration of the antibiotic that inhibits the growth of the bacteria

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9
Q

What is broth microdilation?

A

Cultures of different samples of bacterium. Add broth containing antibiotics in increasing doubling concentrations. MIC is concentration of broth added when sample appears clearer/bacterial culture killed.

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10
Q

What is a minimum inhibitory concentration E test?

A

A strip containing antibiotic at a gradient of concentration. This strip is placed on a contaminated agar plate. Zonal clearing occurs around the strip.
The first number where there is no growth will be the MIC.
Advantage is that is is less time and labour intensive than broth microdilution

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11
Q

What are the 4 different mechanisms of action of antibiotics?

A

Can affect:

  • cell wall synthesis
  • cell membrane function
  • nuclei could acid synthesis
  • protein synthesis
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12
Q

What antibiotics affect cell wall synthesis?

A

Beta-lactams (penicillins, cephalosporins)

Glycopeptides

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13
Q

What antibiotics affect cell membrane function?

A

Polymixins

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14
Q

What antibiotics affects the nuclei acid synthesis?

A

Quinolone
Trimethoprim
Rifampicin

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15
Q

How does penicillin work?

A

Penicillin reacts with penicillin binding protein, a protein that usually forms the cross linking between the cell membrane and the cell wall. The penicillin stops the formation of cross linking between the cell membrane and the cell wall. This weaken the bacterial wall, allowing influx of water and lysis of the bacterium.

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16
Q

How does vancomycin work?

A

Vancomycin binds with the nucleic acid chains between the cell wall and the cell membrane. As vancomycin is blinded to these nucleic acid strands, the cell wall cross-linking enzyme cannot attach, and therefore no cross linkages are made. Cell wall is then weakened and lysis occurs.

17
Q

What are the 3 different types of resistance?

A

Intrinsic

  • no target or access for the drug
  • usually permanent

Acquired

  • Acquires new genetic material or mutates
  • usually permanent

Adaptive
- The organism responds to stress (subinhibitory level of the antibiotic

18
Q

What are the 3 mechanisms of resistance?

A
  1. Enzymatic modification or destruction of antibiotics
  2. Enzymatic alteration of antibiotic targets
  3. Mutations of bacterial target sites
19
Q

How do antibiotics promote chromosomal gene mutation?

A

When bacteria are exposed to antibiotics, if there is a bacteria present that has a chromosomal gene mutation that provides resistance to the antibiotic then it will not be destroyed by the antibiotic. Only the unmutated bacteria are removed. This leaves the mutated bacterium with less competition, so it can go on the replicate at an increased rate.

20
Q

What are plasmids?

A

small circular DNA molecules. Bacteria can pick up new plasmids from other bacterial cells (during conjugation) or from the environment. They can also readily lose them – for instance, when a bacterium divides in two, one of the daughter cells might miss out on getting a plasmid.

21
Q

Describe horizontal gene transfer

A

One bacterium can transfer plasmids to another recipient bacterium. They can be bacterium of different species. This allows different genes and therefore properties to be transferred from one species of bacteria to another, such as resistance.

22
Q

What are commonly used Beta-lactams?

A

Penicillins
Cephalosporins
Carbapenems
Monobactams

23
Q

What are the main functions of penicillin?

A

Penicillin
-Narrow spectrum. Effective against Streptococci.

Amoxicillin
- also some activity against gram negative

Flucloxacillin
- active against staphylococci and streptococci

24
Q

What are B-lactamase inhibitor combinations?

A

Combinations of penicillins and beta-lactamase inhibitors.
Used to treat UTI’s
Co-amoxiclav
Piperacillin

25
Q

What are cephalosporins?

A

Type of penicillin.
More effective agains gram negative, still effective against gram positive.
Broad spectrum
No anaerobes activity
Good activity in CSF so can treat meningitis in the bowel

26
Q

Why is there concern over cephalosporin usage?

A

As it also is effective against bacteria in the bowel, and therefore as there is less competition in the bowel and C.diff proliferates

27
Q

What are Carbapenems?

A

A type of penicillin (meropenem, ertapenem, imipenem)
Very broad spectrum
Effective against negative gram
Safe in penicillin allergy
Reserve antibiotic for gram-negative infection

28
Q

What are glycopeptides?

A

A class of penicillin. Includes Vancomycin and Teicoplanin.
Vancomycin
-most effective against gram positive
-Some Enterococci resistant.
-Not absorbed, so must be given orally if treating c.diff.
-Therapeutic drug monitoring required dust to narrow therapeutic region

Teicoplanin
-similar to vancomycin but easier to administer due to less regular testing.

29
Q

Describe tetracycline and doxycycline

A
  • similar spectrum
  • oral only
  • broad spectrum
  • use during penicillin allergy
  • Usually used for Gram +ve
  • Active in pneumonia, chlamydia and some Protozoa.
  • stain teeth so shouldn’t be given to children, pregnant or breastfeeding women.
30
Q

Describe aminoglycosides

A

Commonly gentamicin
Effective against gram negative
Good activity in the blood/urine
Only works well in oxygenated areas
Therapeutic drug monitoring required (toxins in high concentration affects balance long term)
Reserved for severely gram negative gram negative sepsis

31
Q

Describe macrolides

A

Example is erythromycin
Intracellular penetration so well distributed in cells
Effective against gram positive
Alternative against penicillin
Active against atypical respiratory pathogens

32
Q

Describe quinolones

A 
Example is ciprofloxacin
Effective against gram negative
Active against atypical bacterium
Good bioavailability 
Mechanism is by inhibiting DNA gyrase
Increasing levels of resistance 
Risk of developing c.diff 
LOTS of negative side effects (associated with tendinitis and rupture, aortic dissection and CNS effects)
33
Q

Describe Trimethoprim and sulphonamides

A

Inhibitors of folic acid synthesis
Trimethoprim used for UTI in the UK
Has activity against MRSA

34
Q

Describe Azoles

A

A type of antifungal
Inhibits cell-membrane synthesis
Fluconazole used to treat candida
Morse side effects than with antibiotics

35
Q

What are polyenes?

A

Antifungals
Examples are (my statin and amphotericin)
Inhibit cell membrane function
Nystatin used as a topical treatment of candida
Amphotericin for IV treatment of systemic fungal infections

36
Q

Describe some antivirals

A

Aciclovir

  • when phosphorylated it inhibits viral DNA polymerase
  • treats herpes, chicken pox and shingles

Oseltamivir

  • also known as tamiflu
  • Effective against influenza A and B
37
Q

Describe Metronidazole

A

An antibiotic and antiprotozoal agent

  • active against anaerobic bacteria
  • active against protozoa
  • shouldn’t drink on these antibiotics
38
Q

What can be used to check antibiotic prescribing in the UK?

A

Rx Guidelines

Infection. (10 decks)

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