Antibiotics and antifungals

Question 1

General info about background

Answer 1

Single-cell microorganisms - cell wall & cell membrane
An entire phylogenetic domain
~ 1/3 are pathogenic

Question 2

Differentiate gram +ve and gram -ve bacteria

Give an important example of each

Answer 2

Gram Positive Bacteria
Prominent peptidoglycan cell wall
E.g. Staphylococcus Aureus

Gram Negative Bacteria
Outer membrane with lipopolysaccharide
E.g. Escherichia Coli

Question 3

What is mycolic bacteria

Answer 3

Outer mycolic acid layer
E.g. Mycobacterium Tuberculosis

(kind of seen as gram +ve)

Question 4

Outline nucleic acid synthesis in prokaryotes

Answer 4

Dihydropteroate (DHOp)

• Produced from paraaminobenzoate (PABA)
• Converted into dihydrofolate (DHF)

Tetrahydrofolate (THF)

• Produced from DHF by DHF reductase
• THF –> Important in DNA synthesis

Question 5

Outline an important mechanisms in DNA replication

Answer 5

DNA gyrase
-Topoisomerase –> releases tension

Allows access of other enzymes

Question 6

Outline important mechaisms in RNA synthesis

Answer 6

RNA polymerase

Produces RNA from DNA template

`Differ from eukaryotic RNA polymerase

Question 7

Outline important mechasnism of the protein synthesis

Answer 7

Ribosomes

Produce protein from RNA templates

Differ from eukaryotic ribosomes

(30S and 50S)

Question 8

How do sulphonamides work

Answer 8

Sulphonamides inhibit DHOp synthase (Dihydropteroate)

To reduce DNA synthesis

Question 9

How do trimethoprim work

Answer 9

Trimethoprim inhibits DHF reductase

To reduce DNA….

Combination with sulphonamide used sometimes

Question 10

How do quinolones/fluoroquinolone work

Give an example

Answer 10

Fluoroquinolones (e.g. Ciprofloxacin) inhibit DNA gyrase & topoisomerase IV

Cannot replicate DNA if the DNA is not unwound

Question 11

How to rifamycins work

What is it used to treat

Answer 11

The rifamycins (e.g. Rifampicin) inhibits bacterial RNA polymerase

Prevents RNA and thus protein production, so the bacteria cannot produce elements needed to survive.

Drug interaction–> CYP450 enzyme inducer (along with carbamazepine)

Used to treat TB

Question 12

Which drugs affect the ribosomes

Answer 12

Aminoglycosides (e.g. Gentamicin)
Chloramphenicol
Macrolides (e.g. Erythromycin)
Tetracyclines

Question 13

Drug interactin of erythromycin

Answer 13

Erythromycin and related ABs are CYP450 INHIBITORS

So is ciprofloxacin (a flouroquinolone) and related ABs

as well as ketoconazole

and cimetidine (like ranitidine)

Question 14

Outline peptidoglycan cell wall synthesis

Answer 14

A pentapeptide is created on N-acetyl muramic acid (NAM)

N-acetyl glucosamine (NAG) associates with NAM forming PtG

Happens within the cytplasm

Question 15

Outline PtG transport

Answer 15

The peptidoglycan is produced within the cytoplasm, so needs to be transported through the membrane into the cell wall

PtG is transported across the membrane by bactoprenol

Question 16

Outline PtG incorporation

Answer 16

Now the PtG has made it to the cell wall, it needs to be incoroporated

PtG is incorporated into the cell wall when transpeptidase enzyme cross-links PtG pentapeptides

Question 17

Function of glycopeptide drugs

Give an example

Answer 17

Glycopeptides (e.g. Vancomycin) bind to the pentapeptide preventing PtG synthesis

Question 18

Which drug targets PtG transportation

Answer 18

Bacitracin inhibits bactoprenol regeneration preventing PtG transportation

Question 19

Which drugs target PtG incorporation

Give examples of PtG incorporation

Answer 19

b-lactams bind covalently to transpeptidase inhibiting PtG incorporation into cell wall

Carbapenems
Cephalosporins
Penicillins

Question 20

Outline drugs affect cell wall stability and how they work. Give an example of each

Answer 20

THIS INVOLVES CHANGING THE MEMBRANE WHICH AFFECTS CELL WALL STABILITY

Lipopeptide - (e.g. daptomycin) disrupt Gram +ve cell WALL

Polymyxins - binds to LPS & disrupts Gram -ve cell MEMBRANE

Question 21

Causes of antibiotic resistance

+ list the methods of AB resistance

Answer 21

Unnecessary prescription
(~ 50% of antibiotic prescriptions not required)

Livestock farming
(~ 30% of UK antibiotic use in livestock farming)

Lack of regulation (OTC availability in Russia, China, India)

Lack of development
(Very few antibiotics in recent years)

1. Production of destruction enzymes
2. Additional targets
3. Alter the target site
4. Hyperproduction
5. Alterations in drug permeation

Question 22

Outline production of destruction enzymes

Answer 22

b-lactamases hydrolyse C-N bond of the b-lactam ring

Question 23

Give examples of ABs which are, and those which ARE NOT affected by beta-lactamases

What is amoxiclav

Answer 23

ARE: penicillin G and V

ARE NOT: Flucloxacillin & Temocillin are b-lactamase resistant (I.E. NOT AFFECTED BY BETA LACTAMASE)

Amoxicillin is Broad spectrum (which on it’s own is susceptible to beta lactamases)

• Gram -ve activity
• Co-administered with Clavulanic acid (this is a beta lactamase INHIBITOR, so stops the AB from being broken down)

Question 24

Outline resistance due to additional target with example

Answer 24

Bacteria produce another target that is unaffected by the drug

E Coli produce different DHF reductase enzyme making them resistant to trimethoprim

Question 25

Outline resistance due to alteration target enzymes with example

Answer 25

Alteration to the enzyme targeted by the drug. Enzyme still effective but drug now ineffective

S Aureus - Mutations in the ParC region of topoisomerase IV confers resistance to quinolones

Question 26

Outline resistance due to hyperproduction with example

Answer 26

Bacteria significantly increase levels of DHF reductase

E Coli produce additional DHF reductase enzymes making trimethoprim less effective

Question 27

Outline alterations in drug permeation as a resistance mechanism

Give examples

Answer 27

Reductions in aquaporins & increased efflux systems

Primarily of importance in gram –ve bacteria

Question 28

Classify fungal infectins

Answer 28

Superficial - Outermost layers of skin

Dermatophyte - Skin, hair or nails

Subcutaneous - Innermost skin layers

Systemic - Primarily respiratory tract

Question 29

2 types of antifungals

Answer 29

Azoles: Fluconazole
Polyenes: Amphotericin

Question 30

Mechanism of azoles action

Give an example

Answer 30

Inhibit cytochrome P450-dependent enzymes involved in membrane sterol synthesis

Fluconazole (oral)  candidiasis & systemic infections

(similar to vancomycin)

Question 31

Mechanism of polyenes action

Give an example

Answer 31

Interact with cell membrane sterols forming membrane channels, to disrupt cell wall

Amphotericin (I-V) –> systemic infections