4. Antimicrobials

Question 1

What are the 4 classes of antimicrobials?

Answer 1

Antibacterial
Antifungal
Antiviral
Antiprotozoal

Question 2

What are the 4 ways of classifying antibacterial agents?

Answer 2

Bactericidal or bacteriostatic
Spectrum - broad v narrow
Target site
Chemical structure (antibacterial class)

Question 3

Give 6 ideal features of antimicrobial agents

Answer 3

Selectively toxic
Few adverse effects
Reach site of infection
Oral/IV formulation
Long half-life
No interference with other drugs

Question 4

What are the 4 antibacterial mechanisms of action? Give one example of a class of antibacterial for each

Answer 4

Interfere with:
Cell wall synthesis - beta-lactams 
Cell membrane function - polymixins
Protein synthesis - tetracyclines
Nucleic acid synthesis - quinolones

Question 5

How does penicillin interfere with cell wall synthesis?

Answer 5

Binds to penicillin binding protein, blocking it, and preventing it from forming the crosslinks between peptidoglycans in the cell wall

Question 6

What are the 3 types of antimicrobial resistance and how do they work? Are they permanent or reversible?

Answer 6

Intrinsic - no target or access for the drug. Permanent.
Acquired - acquires new genetic material or mutates. Permanent.
Adaptive - organism responds to stress (low levels of antibiotics). Reversible.

Question 7

What are the 3 mechanisms of resistance?

Answer 7

Drug inactivating enzymes
Target enzyme has lowered affinity for antibacterial
Decreased permeability or increased efflux

Question 8

What are the two ways that genetic alterations can lead to antibiotic resistance?

Answer 8

Chromosomal gene mutation

Horizontal gene transfer (conjugation, transduction or transformation)

Question 9

How can you measure antibiotic activity?

Answer 9

Disc testing

Question 10

How do you work out the minimum inhibitory concentration of an antibiotic?

Answer 10

Vials with different concentrations of antibiotic. Put organism into broths and see if grows. MIC is the tube with the lowest antibiotic conc where no organism grows. (Remember to do two controls - no antibiotic, but one with organism and one without)

Question 11

What is penicillin active against?

Answer 11

Streptococci

Question 12

What is flucoxacillin active against?

Answer 12

Staphylococci and streptococci

Question 13

What is the most broad spectrum antibiotic? What is it active against?

Answer 13

Meropenem
Most gram negatives
(Usually safe in penicillin allergy)

Question 14

What is vancomycin active against? What is required when using the drug?

Answer 14

Gram positives

Therapeutic drug monitoring

Question 15

What class of antibiotics should be given to children under the age of 12 as they stain teeth and bone yellow?

Answer 15

Tetracyclines

Question 16

What is trimethoprim used for? How does it work?

Answer 16

UTI

Inhibitor of folic acid synthesis as part of nucleic acid synthesis mechanism of function

Question 17

What are the two main groups of antifungals and how do they work?

Answer 17

Azoles - inhibit cell-membrane synthesis eg fluconazole for Candida
Polyenes- inhibit cell membrane function

Question 18

How does the main class of antivirals, aciclovir, work?

Answer 18

Inhibits viral DNA polymerase when phosphorylated

Question 19

What two types of microbes is metronidazole active against?

Answer 19

Anaerobic bacteria

Protozoa