Antimicrobials

Question 1

Four ways to classify antibacterial agents?

Answer 1

Bactericidal or Bacteriostatic (Prevents growth and replication)
Spectrum- Broad or Narrow
Target site
Chemical structure

Question 2

What are the ideal features for an antimicrobial agent? 5

Answer 2

Selectively toxic
few side effects
reach the site of infection
Long half life (Infrequent dosing)
No interference with other drugs

Question 3

What four aspects of bacteria can antibacterials acct on?

Answer 3

Cell wall synthesis
Cell membrane function
Protein Synthesis
Nucleic Acid

Question 4

How does penicillin act on bacterial cell wall?

Answer 4

Peptidoglycan
cross linking by penicillin bonding protein
Penicillin slots into binding protein so cannot do it job of forming cross links

Question 5

How does vancomycin act on the bacterial cell wall?

Answer 5

Vancomycin sits on the two side chains of peptidoglycans

Blocks the site so pencillin binding protein can’t bind

Question 6

What are the three types of resistance?

Answer 6

Intrinsic- No target or access for the drug, permanent
Acquired- Acquires new genetic material, usually permanent
Adaptive- Organism responds to stress (Eg low concentration of antibiotic). Usually reversible

Question 7

3 mechanisms of resistance?

Answer 7

Drug inactivating enzymes
Altered target- decreased affinity of enzyme for antibacterial
Altered uptake- Decreased permeability, or increased efflux

Question 8

Two genetic bases for antibiotic resistance?

Answer 8

Chromosomal gene mutation

Horizontal gene transfer

Question 9

Explain chromosomal gene mutation as a mechanism for developing antibiotic resistance

Answer 9

Mutation in one bacteria so this bacteria is resistant
Antibiotic kill the susceptible bacteria
So the resistant bacteria can now replicate and for a new, resistant colony

Question 10

Describe horizontal gene transfer

Answer 10

Three avenues:

1. Conjugation- Straight from one bacteria to another through the cell walls through a hole called a porin
2. Transduction- DNA is transferred using a bacteriophage virus vector
3. Transformation- Free DNA that is just in the extracellular enviroment can just enter the bacteria

Question 11

How would yoou measure the effectiveness of drugs?

Answer 11

Find the minimum inhibitory concentration
number of test tubes
A control with no antibiotic or bacteria to check for contamination
then an number of test tubes, each test tube doubling the concentration of drug.
Find the minimum concentration that prevents bacterial growth
This is the minimum inhibitory concentration

Question 12

What group of bacteria are penicillins active agaist?

Answer 12

Gram positive

Question 13

What drug is used to treat meningitis and why?

Answer 13

Cetriaxone

Good activity in the CSF

Question 14

What group of antimicrobial is vancomycin? What group of bacteria is it most effective against?

Answer 14

Glycopeptide

Active against most gram positive