Antibiotics

Question 1

What is the chemotherapeutic index?

Answer 1

Chem Index = maximum tolerated dose / minimal effective dose

Question 2

What is an antibiotic?

Answer 2

A substance produced by a living organism that inhibits other microorganisms growth/reproduction

Question 3

What is a chemotherapeutic agent?

Answer 3

An artificially created antimicrobial substance

Question 4

How do you measure bacteriostatic activity? (antibiotic susceptibility)

Answer 4

MIC (minimal inhibitory concentration)

Question 5

How do you measure bactericidal activity? (antibiotic susceptibility)

Answer 5

MBC (minimal bactericidal concentration)

Question 6

List bacteriostatic antibiotics:

Answer 6

• macrolides
• tetracyclines
• chloramphenicols
• sulfonamides

Question 7

List bactericidal antibiotics:

Answer 7

-beta-lactams
- aminoglycosides
-rifamycins
-glycopeptides
fluoroquinolones

Question 8

What do aminoglycosides typically target?

Answer 8

Gram negative bacteria (usually aerobic)

ex. streptomycin (in TB)

Question 9

What is the mode of action of aminoglycosides?

Answer 9

Inhibit protein synthesis by binding to the 30S ribosomal subunit

Question 10

What are adverse effects of ahminoglycosides?

Answer 10

• ototoxicity (ear)

- nephrotoxicity

Question 11

How are aminoglycosides administered?

Answer 11

Given parenterally

–> injection or infusion

Question 12

How can you determine MIC?

Answer 12

Use the E-test

Question 13

What is the E-test?

Answer 13

A quantitative test for antimicrobial susceptibility and MIC in gram + and -ve aerobic bacteria
- Combines the dilution and diffusion method

Question 14

Give examples of fastidious bacteria

Answer 14

Anaerobes:

• n. gonorrhea,
• s. pneumoniae,
• streptococcus

Question 15

What is the Kirby Bauer test?

Answer 15

Agar diffusion test

–> To test the bacteria’s sensitivity to antibiotic

Question 16

What is the zone of inhibition?

Answer 16

The area where the antibiotic has killed the bacteria in an agar diffusion test
–> the larger the “ring” the more the antibiotic diffused and stopped growth/killed the bacteria

Question 17

Explain the diffusion test:

Answer 17

• Make bacterial lawn from McFarland sample on agar plate
• Place paper discs w/ antibiotics on lawn
• Incubate overnight 37 degrees
• Look @ inhibition zones (different mm indicate susceptibilities)

Question 18

Where do you find the MIC in an E- test?

Answer 18

Where the edge of inhibition ellipse intersects the side of the strip

Question 19

List the 30S ribosomal subunit protein synthesis inhibitors:

Answer 19

• aminoglycosides

- tetracyclines

Question 20

List the 50S ribosomal subunit protein synthesis inhibitors:

Answer 20

• macrolides
• lincosamides
• streptogramins
• chloramphenicol
• oxazolidinones