Antimicrobial resistance

Question 1

Gram positive bacterial stain what colour?

Answer 1

Purple

Question 2

Gram negative bacteria stain which colour?

Answer 2

Pink

Question 3

Give an example of how susceptibility/resistance could be Determined?

Answer 3

Disc diffusion - zone of inhibition around an antibiotic disc
Doesn’t show HOW resistant they are, only that they are resistance

Question 4

What is the MIC?

Answer 4

Minimum inhibitory conc of a drug = the minimum conc of a chemical that prevents the growth of bacteria

Question 5

When using microtitre plates what do cloudy and clear wells show?

Answer 5

Cloudy - bacteria has been able to grow in that conc of antibiotic
Clear - no growth of bacteria

Question 6

What are E-test strips and how are they used?

Answer 6

Strips that have an increasing conc of antibiotic

Placed into bacterial agar, where growth stops the conc is defined as the MIC

Question 7

Apart from the MIC what other factors need to be considered when selecting an antibiotic?

Answer 7

• location of infection: lipid soluble reach higher levels in tissue than they do in serum
• Some are more effective against gram +ve than gram -ve

Question 8

What 3 steps must antimicrobials complete to be effective?

Answer 8

• Must reach the binding site
• Must attach to the binding site
• Must be able to occupy the binding site for long enough

Question 9

Give 2 examples of conc dependant antimicrobials

Answer 9

Aminoglycosides

Fluoroquinolones

Question 10

Give 3 examples of time dependant antimicrobials

Answer 10

Cephalosporins
Penicillins
Tetracyclines

Question 11

Give an example of a conc and time dependant antimicrobial

Answer 11

Clindamycin

Question 12

Synergism can help prevent what and how?

Answer 12

Antimicrobial resistance

because of lower doses of antimicrobials because of their potent combined effects

Question 13

When are microorganisms classed as resistant?

Answer 13

When the MIC exceeds the amount of drug that can be successfully achieved in the body

Question 14

What is the MPC?

Answer 14

Mutant prevention concentration
the lowest drug conc required to block the growth of the least susceptible cell present in high density bacterial populations

Question 15

What is the mutant selection window?

Answer 15

The danger zone for therapeutic drug conc

- minimising the time spent in this window may reduce the likeliness for resistance

Question 16

What is the main method of resistance in gram negative bacteria?

Answer 16

Plasmid transfer

Question 17

Multi-drug resistance is defined as?

Answer 17

Resistance to drugs belonging in 3 or more distinct drug classes

Question 18

By what methods can the bacteria become adapted to resistance?

Answer 18

• Decrease permeability: drugs can not longer pass into the cell
• Efflux: able to reduce the intracellular conc of a drug
• Inactivation: produce an enzyme to destroy the antibiotic
• Alter the target so the antibiotic cannot bind

Question 19

Give some examples of biofilms

Answer 19

wounds
ear infections
urinary tract infections
endocarditis 
indwelling devices

Question 20

What is the advantage to bacteria when in a biofilm?

Answer 20

Evade host defences and withstand antimicrobial therapy

Question 21

Which layer of the biofilm is protective of the bacteria?

Answer 21

Polysaccharide