2- Principles of anti-microbial resistance

Question 1

Describe the disk diffusion method

Answer 1

A disk of antibiotics with a set concentration of antibiotic = antibiotic gradient from the disk

Measure the zone of inhibition from the disk = zone where the bacteria will not grow and measures the susceptibility of the bacteria tot he antibiotic

Question 2

Define clinical breakpoint values

Answer 2

Value to know if a bacterium is sensitive or resistance to a drug = where does the MIC sit within this range

Question 3

Define intrinsic resistance & give an example of this

Answer 3

Innate ability to resist the activity of an antimicrobial agent (lacks target/altered target so never sensitive)

• Mycoplasma lack a cell wall so cell wall targeting antibiotics are useless

Question 4

Give 3 examples of acquired resistance

Answer 4

Alteration of drug
- Degradation
Alteration of target
Bypass mechanism
Efflux systems

Question 5

What type of antibiotic is often destroyed by beta-lactamase? (Enzymes produced by bacteria)

Answer 5

Simple penicillin

Question 6

Main resistance mechanism of tetracyclines

Answer 6

Efflux (bacteria pumps out toxic substances)

Question 7

Main resistance mechanisms of aminoglycosides

Answer 7

Enzymatic modification
Ribosomal mutations

Question 8

List 3 causes of antibiotic therapy failure

Answer 8

unjustified therapy
poor selection of antibiotics
wrong dose
supressed host response
resistance

Question 9

List 2 ways in which antimicrobial resistance can be assessed

Answer 9

liquid culture MIC determination
disk diffusion
detection of known resistance genes or mutatiosn

Question 10

What is MSC

Answer 10

minimum selective concentrations
the concentration at which there is no therapeutic effect but there is still selective advantage to being resistant or susceptible. As the resistant bacteria start outgrowing their sensitive counterparts

Question 11

What is acquired resistance

Answer 11

when a microorganism obtains the ability to resist the activity of a drug. can be mutation or new gene acquisition

Question 12

List 2 examples of intrinsic resistance

Answer 12

poor permeability due to outer membrane
target different to other Genera
lack target

Question 13

list 2 factors that increase risk of resistant bacteria being selected

Answer 13

underdosing
length of selective level
presence of resistant bacteria to select