Antibiotics and Anti-fungals Flashcards

1
Q

Describe the distinctive features of:

a. Gram positive bacteria
b. Gram negative bacteria
c. Mycolic bacteria

A
a. Gram positive bacteria 
Thick peptidoglycan cell wall 
b. Gram negative bacteria 
Outer membrane that contains lipopolysaccharide (LPS)
c. Mycolic bacteria  
Outer mycolic acid layer
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2
Q

State the steps involved in the production of THF from PABA.

A

PABA –> DHOp (enzyme = dihydropterase synthase)
DHOp –> DHF
DHF –> THF (enzyme = DHF reductase)

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3
Q

What is DNA gyrase?

A

A type of topoisomerase (topoisomerase II)

It releases tension in DNA and is important in unwinding DNA to allow protein binding required for DNA replication

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4
Q

What does RNA polymerase do?

A

Produces RNA from a DNA template

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5
Q

What is the key difference between ribosomes in eukaryotes and prokaryotes?

A

Eukaryote = 40S + 60S Prokaryote = 30S + 50S

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6
Q

State two classes of drugs that interfere with nucleic acid synthesis and name the enzymes that they inhibit.

A

Sulphonamides – inhibits dihydropterate synthase

Trimethoprim – inhibits DHF reductase

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7
Q

These two drugs are sometimes used together. What is this preparation called?

A

Co-trimoxazole

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8
Q

Name a group of drugs that interfere with DNA replication and state its targets.

A

Fluoroquinolones (e.g. ciprofloxacin) inhibits bacterial DNA gyrase and topoisomerase IV

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9
Q

Name a group of drugs that interfere with RNA synthesis and state its main target.

A

Rifamycins (e.g. rifampicin) – inhibits RNA polymerase

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10
Q

List 4 groups of drugs that interfere with ribosomes.

A

Macrolides
Chloramphenicol
Aminoglycosides
Tetracyclines

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11
Q

Describe how peptidoglycan is synthesized, transported to the cell wall and incorporated into the cell wall.

A

A pentapeptide is created on N-acetyl muramic acid (NAM)
N-acetyl glucosamine (NAG) associates with NAM forming peptidoglycan
The peptidoglycan is then transported into the cell wall by bactoprenol
The peptidoglycan is then incorporated into the cell wall by transpeptidase enzyme, which cross-links the peptidoglycan pentapeptides

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12
Q

Which groups of drugs interfere with peptidoglycan synthesis and how do they do this?

A

Glycopeptides (e.g. vancomycin) – they bind to the pentapeptides and inhibit peptidoglycan synthesis
This is used as a last resort for Gram-positive bacteria that are resistant to other antibiotics

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13
Q

Name a drug that interferes with peptidoglycan transport andstate its target.

A

Bacitracin – this inhibits bactoprenol, hence preventing peptidoglycan transport

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14
Q

Name a class of drugs that inhibit peptidoglycan incorporation and explain how they do this.

A

Beta lactams – they bind covalently to transpeptidase, which inhibits peptidoglycan incorporation into the cell wall

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15
Q

What are the three subsets of beta lactams?

A

Carbapenems
Cephalosporins
Penicillins

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16
Q

Name two drugs that interfere with cell wall stability and explain how they do this.

A

Lipopeptides – disrupt Gram-positive cell walls

Polymyxins – bind to lipopolysaccharide and disrupt Gram-negative cell membranes

17
Q

List five mechanisms of antibiotic resistance and give a brief description of each.

A

Additional target– the bacteria produce another target that is unaffected by the drug
Hyperproduction – the bacteria increase the production of the target so the antibiotics are less effective (this is energy inefficient)
Altered target site – there is an alteration in the drug target so that the drug is no longer effective
Alteration in drug permeation– down regulation of aquaporins (responsible for allowing drugs into cells) or the upregulation of efflux systems
Production of destruction enzymes– beta-lactamases hydrolyse the C-N bond in the beta-lactam ring rendering the beta-lactams inactive

18
Q

What are penicillins G and V normally used to treat?

A

Gram-positive bacteria

19
Q

Name two drugs that are relatively beta lactamase resistant.

A

Flucloxacillin and temocillin

20
Q

Name a broad-spectrum antibiotic that must be administered with another drug to become resistant to beta lactamases. What is this other drug?

A

Amoxicillin (no antibiotic resistance on its own)

Clavulanic acid

21
Q

What are the two courses of treatment for mycobacterial infections?

A

Isoniazid + Rifampicin (6 months)

Ethambutol + Pyrazinamide (2 months)

22
Q

What are the mechanisms of action of isoniazid and rifampicin?

A

Isoniazid – inhibits mycolic acid synthesis

Rifampicin – inhibits RNA polymerase

23
Q

What else is rifampicin indicated for?

A

Leprosy

24
Q

What are the four types of fungal infection, characterised based on the tissues/organs affected?

A

Superficial – outermost layers of skin
Dermatophyte – skin, hair or nails
Subcutaneous – innermost skin layers
Systemic – primarily respiratory tract

25
Q

What are the two main groups of anti-fungals? Give an example ofeach.

A

Azoles (fluconazole)

Polyenes (amphotericin)

26
Q

Describe the mechanism of action of azoles.

A

They inhibit CYP51p (enzyme of the CYP450 system), which is involved in ergosterol production

27
Q

Describe the mechanism of action of polyenes.

A

These interact with membrane sterols and form channels (punching holes in the membrane)