L1 antibiotics

Question 1

anti infective drugs

Answer 1

Anti-infective drugs - antimicrobials 
		○ Antibacterials 
		○ Antivirals 
		○ Antifungals 
		○ Antiprotozoals 
		○ Antihelminths

Question 2

• Antibiotic

Answer 2

○ A chemical produces by a microorganism that kills or inhibits ither microorganisms
○ Synthetic or semisynthetic antimicrobials are not strictly antibiotics by definitions

Question 3

In common clinical usage and antibiotic is

Answer 3

§ Agent active against bacteria
§ Natural, synthetic or semisynthetic
§ Done not include antiseptics or disinfectants

Question 4

most antibiotics are from

Answer 4

○ Most antibiotics are products of bacteria or fungi that live in the soil

Question 5

microbes that produce antibiotics

Answer 5

○ Microbes make these compounds in order to kill or inhibit other microbes that are competing for nutrients
○ The microbes which produce these compounds have also developed mechanisms to prevent themselves being killed by them (ie. Resistance mechanisms)

Question 6

semisynthetic antibiotic

Answer 6

emisynthetic antibiotic

§ Based on a natural antibiotic scaffold with chemical modifications

Question 7

synthetic antibiotic

Answer 7

○ Synthetic

§ Not common

Question 8

4 beta lactams

Answer 8

• Penicillins
  Cephalosporins
  Monobactams
  Carbapenems

Question 9

what does transpeptidase do

Answer 9

joins together peptidoglycan precursors onto the growing cell wall

Question 10

3 steps for the transpeptidase to join the peptidoglycan precursors to the cell wall

Answer 10

□ Breaks off one of the d alanines
□ Joins the pentapeptide onto the growing chain
□ Joins the sugars

Question 11

how do beta lactam antibiotics work

Answer 11

B-lactam antibiotics work by binding to transpeptidase and stops it from working

Question 12

another word for transpeptidase

Answer 12

Transpeptidase and called penicillin binding proteins PBPs

Question 13

• Glycopeptide antibiotics work by

Answer 13

○ work by binding the d ala d ala end of the peptidoglycan precursor
○ As the enzyme cant remove the d ala, the transglycosylase activity of the transpeptidase activity cant proceed
○ If peptidoglycan cant be strengthened and cross linked, cell wall is weakened and bacterial cell bursts under osmotic pressure

Question 14

rifamycins work by

Answer 14

§ Inhibits the enzyme that produce mRNA

Question 15

○ Macrolides, clindamycin, streptogramins, oxazolidinones work by

Answer 15

binds s to 50S part of the ribosome and inhibit protein elogation

Question 16

○ Aminoglycosides work by

Answer 16

§ Binds to 30S part of the ribosomes and cause misreading of the code

Question 17

○ Tetrecyclines, tigecycline work by

Answer 17

§ Block binding of tRNA to 30S part of the ribosome

Question 18

2 antibiotics acting on folate synthesis

Answer 18

• Sulfonamides and trimethoprim

Question 19

antibiotics acting on folate synthesis work by

Answer 19

○ Prevent manufacture of DNA and RNA precursors

Question 20

Co trimoxazole

Answer 20

trimethoprim + suphamethoxazole

Question 21

1 Antibiotic acting on DNA replication and function

Answer 21

Quinolone

Question 22

Quinolone works by

Answer 22

inhibits action of enzymes necessary for DNA replication

Question 23

1 antibiotic acting on cell membrane

Answer 23

daptomycin

Question 24

• Daptomycin works by

Answer 24

○ Has a lipophilic tail
○ Inserts itself into the phospholipid bilayer of the membrane and causes the membrane to depolarise which causes death of the bacterial cell

Question 25

5 ways antibiotics kill bacteria

Answer 25

• work on production/maintenance of the cell wall
• work on protein production
• work on folate synthesis
• work on DNA replication and function
• work on cell membrane

Question 26

• Narrow spectrum

Answer 26

○ Effective against only a few specific bacteria
○ Eg. Flucloxacillin
§ Active against staph aureus and many streps
§ Gram positive antibiotic

Question 27

Broad spectrum antibiotic

Answer 27

○ Effective against a wide range of bacteria, from different groups
○ Eg. Augmentin
§ Aureus, streptococci, enterococci, many gram negative coliforms, haemophilus influenzae

Question 28

• Empirical therapy used when

Answer 28

○ Specimens are not collected for lab investigation
○ While waiting for results of lab investigations
- Empirical therapy generally broader spectrum than directed therapy
- May switch from empirical to directed therapy

Question 29

reasons to name for narrower spectrum

Answer 29

Broad spectrum therapy
○ Encourages bacterial resistance
○ Kills more normal flora
○ Poses greater risk of drug adverse effects

Question 30

MIC

Answer 30

• The minimum inhibitory concentration (MIC)

○ The minimum concentration of an antibiotic that inhibits visible growth of bacteria in an in vitro test system

Question 31

MIC testing process

Answer 31

○ A series of test tubes containing
§ Broth culture medium
§ Decreasing amounts of antibiotic being testes
§ An inoculum of the bacterium being tested (same inoculum into each tube)
○ The tubes are incubated overnight to allow bacterial growth
○ MIC - concentration at which the antibiotic first works

Question 32

instead of doing a formal MIC, what is done instead

Answer 32

• Routine susceptibility tests are done in simplified form, rather than doing a formal MIC in each case

Question 33

process of routine susceptibility test

Answer 33

○ Lawn inoculum of bacterium being tested - Even layer of bacteria
○ ‘paper discs impregnated with a range of antibiotics
○ Incubated overnight and observed once the lawn has grown

Question 34

MIC < 0.12

Answer 34

highly susceptible

Question 35

MIC < 0.05

Answer 35

relatively resistant

Question 36

MIC < 4.00

Answer 36

resistant

Question 37

MIC > 4.00

Answer 37

highly resistant

Question 38

Mechanisms of resistance to antibiotics

Answer 38

Active removal of an antibiotic from a cell
Inhibition of antibiotic entry to target site
Production of enzymes which modify or destroy antibiotics
Alteration of the antibiotic’s target site so it can no longer bind

Question 39

Active removal of an antibiotic from a cell

Answer 39

• Efflux pumps

Bacteria have many different types of energy driven mechanisms to remove substances from the cell

Question 40

Inhibition of antibiotic entry to target site

Answer 40

• Porin channels
  - Water filled channels which control the entry of aqueous molecules into the cell
  - Mutates into a kind of porin channel that doesn’t let the antibiotic in
  - Eg. Pseudomonas aeruginosa
  § Mutation confers resistance to imipenem

Question 41

3. Production of enzymes which modify or destroy antibiotics

Answer 41

§ B-lactamases
□ A large family of enzymes which break the B lactam ring of the antibiotic
□ More than 1000 described
□ Different affinities for different beta lactam antibiotics
□ Penicillinases, cephalosporinases, carbapenemases

Question 42

• Antibiotics resistant to beta lactamase

Answer 42

§ Penicillins that can resist
□ Methicillin, flucloxacillin
§ Cephalosporins that can resist
□ cephalexin and others

Question 43

Normal transpeptidase gene

Answer 43

§ Normal gene called pbpB encodes PBP2

Question 44

mutated transpeptidase gene

Answer 44

§ Mutated gene called mecA encodes PBP2a

Question 45

MRSA

Answer 45

methicilin resistant staph aureus

Question 46

• Route of antibiotic administration

Answer 46

• Oral - PO
  - Parenteral - IV or IM
  - Rectal - PR