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BMSC2210 - Chemotherapy > L7 - Antibacterials : cell envelope > Flashcards

L7 - Antibacterials : cell envelope Flashcards

1
Q

What are antibac drugs that inhibit peptidoglycan synthesis?

A

B-lactams

vancomycin

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2
Q

What are antibac drugs that affects bacterial membranes?

A

polymxin/colistin

daptomycin

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3
Q

What is the structure of peptidoglycan?

A

N-acetylmuramic acid

N-acetylglucosamine

peptide bridge

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4
Q

What happens during peptidoglycan biosynthesis?

A

3 stages

bulk reaction - stage 1 in bacterial cytoplasm

series of Mur enzymes reactions creating peptidoglycan precursors

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5
Q

What is glycosytransfer?

A

polymerisation of the glycan strands

dissacharide portion of the molecule is incorporated into an existing glycan domain

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6
Q

What is transpeptidation?

A

cross linking between glycans by STEM PEPTIDES

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7
Q

What are stem peptides?

A

5 aa residues of both L and D form

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8
Q

What are the final 2 residues of the stem peptides?

A

two D-Alanine residues

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9
Q

what enzymes catalyse the glycosyltransfer and peptidase reaction?

A

same enzymes as the reaction is coupled

penicllin-binding proteins (PBPs)

bi-functional enzymes with separate domains

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10
Q

What are the 2 antibiotic classes that interfere with final stages of cell wall biosynthesis?

A

B-lactams - penicillins, cephalosporins

glycopeptides - vancomycin, teicoplanin

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11
Q

How do glycopeptides act?

A

bind to the D-alanine peptides at the end of stem peptide

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12
Q

How do B-lactams act?

A

bind to the PBP enzyme

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13
Q

What is the B-lactam mechanism of action?

A

broken B-lactam attaches covalently to the key catalytic residue

stops normal role of transpeptidation

cell wall loses mechanical rigidity

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14
Q

What to peptidoglycan hydrolases do?

A

cleavage of PG for expansion of network

NOT inhibited by B-lactams

bacteria still breaks down its own material

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15
Q

What are the clinical applications of B-lactams?

A

extensive use

SAFE

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16
Q

What are side effects of B-lactams?

A

Hypersensitivity - benzylpenicillin

Anaphylactic shock after injection

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17
Q

How does penicillin allergy occur?

A

small breakdown/isomerization of penicillin

benzylpenicillenic acid is produced - quite reactive with lysine residues

penicillin antigen is produced

18
Q

How do B-lactamases mediate resistance to B-lactams?

A

break open ring = inactive

19
Q

Ho are B-lactams protected by clavulanic acid?

A

inactivates the B-lactamase

irreverisble inhibited enzymes (double hit mechanism)

20
Q

Which B-lactamase inhibitor is the best?

A

AUGMENTIN = Clavanulate-Amoxicillin

21
Q

What are properties of penicillins?

A

modify R variable group

R group = how stable the drug is & stability against B-lactamase

22
Q

What are some therapeutic applications of penicillin G?

A

Pneumococcal pneumonia

Syphilis

Gonorrhea

23
Q

Which molecule is the only B-lactam to have 2 R-groups?

A

CEPHALOSPORINS

24
Q

what is the 4th generation cephalosporin?

A

cefepime

25
Q

What are 3 types of CARBAPENEMS?

A

Impienem
Meropenem
Ertapenem

26
Q

What is vancomycin?

A

natural product antibiotic

27
Q

How does vancomycin bind to D-ala-D-ala

A

H-bonding

28
Q

What is the mode of action of vancomycin?

A

PRIMARILY - transglycosylation

SOME - transpeptidation - can sometimes catch the process

29
Q

Can vancomycin act against all bacteria?

A

NO - inactive against gram-neg

30
Q

What are the clinical applications of vancomycin?

A

IV - treat S.aureus, MRSA, gram-pos

good for people hyper-sensititve B-lactam

oral - C.diff

31
Q

What are the adverse side effects of vancomycin?

A

rapid taking = “red-man” syndrome

nephrotoxic

ototoxic

reversible neutropenia & thrombocytopenia

32
Q

What are polymixins B/E?

A

cyclic lipopeptides

use waned in 1980s but making a comeback

33
Q

What is the mode of action of polymyxins?

A

interacts with lipopolysaccharide

penetrate OM

penetrate IM

flip-flop

disrupt integrity

34
Q

Clinical applications of polymyxins?

A

Pseudomonas

inhalation therapy - cystic fibrosis

decontamination of gut

burns

MDR gram-neg infections
VITAL LAST LINE DEFENCE

35
Q

What are side effects of polymyxins

A

no LPS on gram-pos = inactive

neurotoxicity + nephrotoxicity when given parenterally (20-25%)

36
Q

What is Daptomycin

A

cyclic lipopeptide

acyl chain makes the interaction

37
Q

How does daptomycin work?

A

interacts with membrane via acyl chain

Helped by Ca2+ ions

aggregation

membrane depolarisation = leakage + death

38
Q

Why is daptomycin calcium-mediated?

A

otherwise repulsions between head group & membrane would occur

39
Q

What are the applications of daptomycin?

A

complicated skin/ soft tissue infections

IV

40
Q

What are side effects of daptomycin?

A

NOT ACTIVE against gram-neg

muscle toxicity

BMSC2210 - Chemotherapy (17 decks)

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