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5224 > Cell Wall Synthesis Inhibitors I > Flashcards

Cell Wall Synthesis Inhibitors I Flashcards

1
Q

Who isolated penicillin

A

Alexander Fleming in 1928

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2
Q

When was penicillin used clinically

A

1940’s

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3
Q

What are the B-lactam abx?

A
  • Penicillins
  • Cephalosporins
  • Carbapenems
  • Monobactams
    (same MOA for all of the above)
  • B-lactamase inhibitors (assist B-lactams)
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4
Q

What do all penicillins have in common

A
  • B-lactam ring with amide group
  • Thiazolidine ring with two methyl groups and a carboxyl group
  • Differ in R-side chain
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5
Q

Where is the R-side chain attached

A

to the B-lactam ring via the amide group

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6
Q

What is the critical component of penicillins

A
  • the B-lactam ring

- also found in other subclasses of CWSI

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7
Q

MOA of B-lactams

A
  • interfere with peptidoglycan synthesis in BOTH Gram + an Gram -
  • Bind to transpeptidases to inhibit cross-linking = cannot form stable cell wall
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8
Q

What do transpeptidases do

A

perform the final step of peptidoglycan crosslinking

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9
Q

What are Penicillin Binding Proteins? (PBPs)

A

another name for transpeptidase. They bind to penicillin, hence the name

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10
Q

How is the bacterial cell wall built

A
  • consists of peptidoglycan, which is made of polysaccharides that are cross-linked via small peptides.
    Gram - have a few layers
    Gram + have several layers
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11
Q

Which bacteria has an outer membrane

A

Gram -

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12
Q

Final step of peptidoglycan synthesis

A
  • crosslinking of precursor molecules consisting of separate strands with peptides, attached via the peptides
  • process catalyzed by transpeptidases
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13
Q

What do transpeptidases recognize

A
  • terminal D-Ala-D-Ala of a peptide
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14
Q

Is transpeptidase preserved during peptidogylcan synthesis

A

yes

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15
Q

Are B-lactams reversible or irreversible inhibitors of transpeptidase

A

irreversible

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16
Q

What do B-lactams mimic

A
  • the D-Ala-D-Ala portion of the peptide and acylate transpeptidase instead
  • amide bonds mimics the peptide bond btwn the two D-Ala
  • transpeptidase binds the B-lactam instead and is irreversibly inhibited
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17
Q

What is the result of transpeptidase binding a B-lactam

A

cell walls cannot grow or repair anymore. Cell loses shape, leads to lysis, and cell death

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18
Q

is resistance to B-lactams common or uncommon

A
  • resistance is common
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19
Q

General resistance mechanism: Mutate or protect the target and make it insensitive to the abx. How is this specific to B-lactams

A
  • bacterial mutation of transpeptidase to decrease affinity for B-lactams
20
Q

General resistance mech: Decrease access of abx to target. How is this specific to B-lactams

A
  • decreased permeability of cell envelope.

- Active transport of abx out of cell via efflux pumps

21
Q

General resistance mech: Inactivate Abx. How is this specific to B-lactams

A
  • Hydrolysis of B-lactam ring by B-lactamase (MOST COMMON MECHANISM)
22
Q

General resistance mech: Replace the target with another molecule that can do the same job (alternate biochem pathway). How is this specific in B-lactams

A
  • Express an alternative, low-affinity transpeptidase (intrinsic or acquired). E.g. very common in MRSA
23
Q

How are B-lactamases classified

A
  • four classes based on sequence homology
  • A, C, and D are serine enzymes
  • B are metalloenzymes containing Zn(II)
  • serine enzymes are related to PBP’s
24
Q

How are B-lactamases named

A
  • according to their substrate preference
  • penicillinases bind penicillin
  • cephalosporinases bind cephalosporin
  • carbapenemases bind carbapenem
25
Classification of penicillins
- all have the same core, called penam | - all have same MOA (inhibition of transpeptidase by acylation)
26
What is the penam core composed of
fused B-lactam and thiazolidine rings
27
What does identity of R group determine
- antimicrobial activity - absorption - acid stability (drug shouldn't break down before absorbed) - stability to B-lactamases (make R group bulky to resist)
28
Most common adverse effect of penicillin (and cephalosporins and carbapenems)
hypersensitivity reaction
29
How are R-groups introduced
- fermentation | - semisynthtically
30
Penicillin V (VK for potassium)
- broad spectrum (Gram + and Gram -) - 90% of staph aureus in hospitals is resistant - rapidly absorbed - widely distributed - no CSF penetration - rapidly excreted unchanged (problem for resistance)
31
Penicillinase-resistant penicillins
- resistant to hydrolysis and inactivation by staphylococcal penicillinase - Methicillin, Isoxazolyl penicillins, Nafcillin - enzymes can now inactivate these as well
32
Isoxazolyl penicillins
- acid stable and well absorbed - used against penicillinase-producing staph - NOT useful to Gram - bacteria - Penicillinase-resistant penicillins
33
Nafcillin
- irregular oral absorption (inject) - highly resistant to staph penicillinases - Good BBB penetration = can treat meningitis - Penicillinase-resistant penicillins
34
Aminopenicillins
- KNOW augmentin - Gram + and Gram - - More broad spectrum - Useful against menigococci and listeria - rapidly inactivated by B-lactamase - can recover activity by adding B-lactamase inhibitor
35
What is augmentin
Amoxicillin + clavulanic acid Aminopenicillin - R = H
36
Uses of aminopenicillins
- upper respiratory infections - middle ear infections - UTI - meningitis (in combo with Vancomycin and 3rd gen cephalosporin) - salmonella
37
Amoxicillin
- aminopenicillin - R = OH - BBB penetration - rapidly inactivated (see augmentin)
38
Carboxypenicillins
- active against pseudomonas and proteus spp that are resistant to ampicillin - INeffective against staph, enterococcus, Klebsiella, and Listeria - inactivated by B-lactamases
39
Ureidopenicillins: piperacillin
- covers most strains of pseudomonas, non-B-lactamase producing Enterobaceriacea, etc - Broadest spectrum of all penicillins when in combo with B-lactamase inhibitor - used against serious Gram - infections (often nosocomial)
40
What is zosyn
piperacillin + tazobactam
41
why do penicillins produce hypersensitivity
- look like small peptides
42
B-lactamase inhibitors
- technically B-lactams but have very weak antibacterial action (no R-group) - POTENT inhibitors of many (NOT ALL) B-lactamases - give with abx to restore antibacterial properties
43
Three B-lactamase inhibitors
- clavulanic acid - sulbactam - tazobactam
44
How are B-lactamases available? (in what form)
- only in combo with penicillins and cephalosporins | - KNOW: augmentin (amoxicillin-clavulanate)
45
B-lactamase MOA
- acylate serine B-lactamases, five-membered ring opens up and forms second covalent bond with the enzyme. - gets stuck in enzyme, irreversibly inhibiting it

5224 (9 decks)

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