Week 2

Question 1

Name the 6 targets of antibiotic action

Answer 1

Inhibition if protein synthesis
Inhibition of cell membrane function
Inhibition of cell wall synthesis
Inhibition of DNA dependant RNA polymerase 
Disruption of DNA structure 
Interference with other pathways

Question 2

Give examples of and describe the actions of and development of resistance to antibiotics that inhibit protein synthesis

Answer 2

Tetracyclines, aminoglycosides

Inhibition

• Selective activity due to structural differences between ribosomes
• Most bind to either 305/505 subunits

Resistance

• Alteration of target ( intrinsic due to lack of receptor in ribosome)
• Alteration of drug (acquisition of degradative enzymes)

Question 3

Give examples of and describe the actions of and development of resistance to antibiotics that inhibit function of cell membranes

Answer 3

E.g. polypeptides, cationic peptides

Disrupt cell membrane by interacting with phospholipids causing cell membrane leakage

Question 4

Give examples of and describe the actions of and development of resistance to antibiotics that inhibit cell wall synthesis

Answer 4

B Lactams
- stops peptide cross links in wall
Vancomycin
- interacts with cell wall preventive synthesis of NAG polymers
Bacteriotravin
- interfere with dephosphorylationod isoprenyk carriers for cell wall synthesis

Question 5

Give examples of and describe the actions of and development of resistance to antibiotics that interfere with other pathways

Answer 5

Eg sulphonamides

- block folic acid production

Question 6

Give examples of and describe the actions of and development of resistance to antibiotics that inhibit DNA dependent RNA polymerase

Answer 6

Eg Rifampicins

Block initiation of protein synthesis

Question 7

Give examples of and describe the actions of and development of resistance to antibiotics that disrupt DNA structure

Answer 7

Nitromidazoles
- metabolic products react with DNA causing strands to break
Quinolone
- bond to DNA guarded blocking synthesis

Question 8

Give four factors that a drug needs to have to have to be active

Answer 8

Pathogen sensitivity
Reach target
Reach correct conc at target site
Have right conditions to function

Question 9

Describe the effect of being lipid vs water soluble on the activity of a drug

Answer 9

Lipid soluble - can penetrate cells

Water soluble - confined to blood

Question 10

Define the intrinsic mechanism of resistance to antibiotics (and give examples)

Answer 10

Intrinsic - innate ability to resist activity of a particular antimicrobial agent through inherent structural or fuctional characteritics allwowing tolerance to the drug
e.g. poor membrane permeability, differences in or lack of targets.

Question 11

Define the Acquired mechanism of resistance to antibiotics (and give examples)

Answer 11

Acquired - When a microorganism obtains the ability to resist the activity of an antimicrobial. Acquisition may allow drug alteration, target alteration, bypass mechanisms etc. These occur due to mutations modifications and changes in expression levels.

Question 12

Describe the mechanism by which resistance can be propagated in the environment

Answer 12

• Selective pressure leading to the development of resistant populations grown from resistant individuals

Question 13

Describe MDR

Answer 13

MDR - Multi Drug Resistance

Acquired non susceptibility to at least one agent in three or more categories.

Question 14

Describe XDR

Answer 14

XDR - Extensively Drug Resistant

Acquired non susceptibility to at leat on agent in all but two or fewer categories

Question 15

Describe PDR

Answer 15

PDR - Pan Drug Resistant

Acquired non susceptibility to all agents in all categories

Question 16

How can gene transfer allow for resistance?

Answer 16

Plasmids allow transfer of resistance between closely related bacteria through transfer of genes between them.
Transduction and transformation (uptake of naked DNA from the environment)

Question 17

Give three situations where combination antibiotic therapy could be used

Answer 17

Mixed infections, severe conditions and life threatening cases.

Question 18

Adjunctive treatment

Answer 18

Application of other supportive therapy e.g. fluids, surgery, synergistic drugs etc.

Question 19

What can the results of a dilution test tell you?

Answer 19

The minimum inhibitory concentration of an antibiotic.

Question 20

Describe the test can you use to define which antibiotic a specific pathogen will be susceptible to?

Answer 20

Disk diffusion test (Kirby bauer)
- Spread sample in question onto the surface of non selective agar.
Place antibiotic disks around the surface of the agar
Incubate at 37 degrees overnight and areas of no growth = susceptibility

Question 21

What test can be used to obtain a rapid MIC

Answer 21

E-strip diffusion

Question 22

Define MIC

Answer 22

Minimum concentration of the antibiotic which will inhibit the growth of a bacteria.

Question 23

Define MBC

Answer 23

Lowest concentration which will kill a bacterial strain (kill= 99%death)