Lecture 9 - Antibiotics

Question 1

What are antibiotics

Answer 1

1. Antibiotics are used in the treatment and prevention of bacterial growth
2. Kill or stop bacterial growth
3. Not effective against viral infections
4. Classified based on mechanism of action, chemical structure and spectrum of activity
5. Narrow spectrum antibiotics target specific bacteria e.g. gram positive or gram negative
6. Broad spectrum antibiotics treat many different types of bacteria

Question 2

What is technique for identifying if a bacteria is gram positive or negative

Answer 2

1. Violet dye applied
2. Decolourising agent
3. Red dye
4. Gram-positive retain violet dye
5. Gram-negative lose violet dye and appear red

Question 3

What are beta-lactam anitbiotics

Answer 3

1. Broad-spectrum antibiotics

Question 4

Describe how penicillin works

Answer 4

1. Acts by inhibiting the synthesis of peptidoglycan layer of bacterial cell walls by targeting transpeptidase which catalyses the final cross-linking step in peptidoglycan synthesis
2. The beta-lactam moiety of penicillin irreversibly binds to serine residue in the transpeptidase active site

Question 5

Describe discovery and development of penicillin

Answer 5

1. Penicillin G was isolated from penicillium by Flemming 1928
2. Natural penicillin derivatives are produced in mould fermentation
3. Isolation of 6-aminopenicillin (6-APA) allowed for preparation of semi-synthetic penicillin with improvements in bioavailability, spectrum, stability and tolerance

Question 6

Describe biosynthesis of penicillin G

Answer 6

1. 3 different amino acids are coupled to give a tripeptide
2. Then isopenicillin N synthase converts to convert to isopenicillin N
3. This can then produce cephalosporins or can undergo N-acyltransferase to produce penicillin G

Question 7

Where do derivatives of penicillin come from

Answer 7

1. Adding new side chains to 6-aminopenicillanic acid generated new and effective antibiotics
2. Mode of action stays similar

Question 8

What are Cephalosporins

Answer 8

1. Class of beta-lactam anitbiotics derived from fungus Acremonium
2. Cephalosporins disrupt synthesis of peptidoglycan layer forming in the bacterial cell wall
3. Antibiotics are isolated and refined from culture or derived from 7-amionocephalosporic acid (7-ACA)

Question 9

How do you make a variety of Cephalosporins

Answer 9

1. Make cephalosporin C
2. Hydrolyse to produce 7-ACA

Question 10

What is antibiotic resistance

Answer 10

1. Resistance often reflects evolutionary processes which take place during the therapy
2. Antibiotic treatment may select for bacterial strains with a physiologically or genetically enhanced capacity to survive high doses of antibiotics
3. This results in the preferential growth of resistance bacteria
4. Many antibiotics which used to have high efficacy against many bacterial species have become less effective due to increased resistance

Question 11

Describe beta-lactam antibiotic resistance

Answer 11

1. All beta-lactam anitbiotics have a beta-lactam ring in their structure
2. Beta-lactamase enzymes are enzymes capable of hydrolysing the beta-lactam ring and deactivating the molecules antibacterial properties- e.g. penicillinase
3. Since penicillin has been used, Penicillinase production spread to bacteria that previously did not previously produce it or only produced in small quantities
4. Genes encoding these enzymes may be acquired via plasmid-mediated resistance

Question 12

Are beta-lactam antibiotics useless

Answer 12

1. Not all bacteria are resistant to beta-lactam antibiotics
2. In some instances beta-lactam antibiotics can be co-administered with a beta-lactamase inhibitor
3. Current lactamase inhibitors are competitive inhibitors which can be hydrolysed by the lactamase enzyme- block the enzyme which hydrolyse anitbiotics

Question 13

What are 2 beta-lactamase inhibitors

Answer 13

1. Amoxicillin
2. Clavulanic acid
3. Both contain beta-lactam rings

Question 14

What is another method of resistance

Answer 14

1. Penicillin-binding proteins

Question 15

How do penicillin-binding proteins work

Answer 15

1. Some bacteria have developed novel PCP where beta-lactam antibiotics cannot bind effectively and as a result do not disrupt cell-wall synthesis

Question 16

What are examples of bacteria which use PCP mode of resistance

Answer 16

1. Methicillin-resistant Staphylococcus aureus (MRSA)
2. Penicillin-resistant Streptococcus pneumoniae

Question 17

What is ceftaroline fosamil

Answer 17

1. A prodrug of the active metabolite ceftaroline - hydrolysed in situ
2. Can add functionality which may be cleared at active site- gives beneficial properties
3. Ceftaroline has potent in vitro activity against Gram-positive bacteria including methicillin-resistant staphylococcus aureus and streptococcus pneumoniae

Question 18

Describe structure of ceftaroline fosamil

Answer 18

1. Phosphono- group increases solubility of prodrug so can be hydrolysed in situ
2. 1,2,4-thiadiazole ring: Gram negative penetration and affinity for transpeptidase
3. Oxime confers Beta-lactam resistance
4. Lactam inhibits transpeptidase activity
5. 1,3-thiazole ring- anti MRSA activity

Question 19

What are macrolides

Answer 19

1. Natural products from polyketide
2. Large macrocyclic lactone ring attached to one or more deoxy sugar
3. Used to treat gram +ve bacteria infections- protein synthesis inhibitors
4. Broad spectrum antibiotics, substitute for patients with a penicillin allergy

Question 20

What are examples of macrolides

Answer 20

1. Erythromycin
2. Roxithromycin
3. Clarithromycin

Question 21

How is Roxithromycin formed

Answer 21

1. Semi-synthetic macrolide anitbiotic derived from erythromycin
2. Add NH2OH.HCl, Et3N, MeOH to change ketone to N-OH
3. Add ether chloride with acetone - attacks N and adds ether

Question 22

What are ketolides

Answer 22

1. Structurally related to macrolides but are effective against macrolide-resistant bacteria
2. Ketolides have 2 ribosomal binding units and a modified sidechain which makes them poor substrate for efflux-pump mediated resistance

Question 23

What are tetracyclines

Answer 23

1. Protein synthesis inhibitors
2. Comprise a linear fuest tetracyclic nucleus
3. The simplest tetracycline to display antibacterial activity is tetracycline (6-deoxy-6-demethyltetracycline)- Minimum pharmacophore

Question 24

What is resistance to tetrayclines

Answer 24

1. Efflux pumps which eject tetracycline from the cell
2. Ribosomal protection proteins- dislodge tetracycline from the ribosome

Question 25

How can you produce tetracylcine from chlorotetracycline

Answer 25

1. Reduce with H2, Pd/C 2. Removes Cl

Question 26

Which bits of tetracyclines can be modified

Answer 26

1. R groups at top can be substituted for selected bacterial species 2. 4-(R)-amino group is essential for antibacterial activity 3. Substitution of amide by aldehyde or nitriles reduces activity 4. Ion chelation increases anti metallo proteinase activity 5. Non modifiable region- contact side with ribosome- =O/-OH bit

Question 27

What is chloramphenicol

Answer 27

1. Isolated from streptomyces venezuelae 2. First antibiotic to be synthesised rather than isolated 3. Protein synthesis inhibitor

Question 28

What is resistance to chloramphenicol

Answer 28

1. Reduced membrane permeability to low levels of chloramphenicol 2. Acquisition of the cat-gene which encodes chloramphenicol acetyltransferase

Question 29

How does antibiotic resistance occur

Answer 29

1. High number of bacteria, where a few are resistant to antibiotics 2. Antibiotics kill bacteria causing the illness, as well as good bacteria protecting the body from infection 3. The resistant bacteria now have preferred conditions to grow and take over 4. Bacteria can even transfer their drug-resistance to other bacteria through plasma transfer

Question 30

What are the different categories that WHO uses to tackle antibiotic resistance

Answer 30

1. Access 2. Watch 3. Reserve

Question 31

What is access category

Answer 31

1. Those listed as first and second choice for empiric treatment of the most common infection syndromes 2. Antibiotics that should be consistently globally widely available

Question 32

What is Watch category

Answer 32

1. Generally have higher toxicity concerns and resistance potential 2. E.g. penicillins with beta-lactamase inhibitor, macrolides, cephalosporins older

Question 33

What is Reserve category

Answer 33

1. Includes new antibiotics and 'last-resort' treatment options 2. Should be protected and prioritised as key targets of high-intensity nation and international stewardship programs to preserve effectiveness 3. E.g. cephalosporins newer