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Pharmacology -- Test #2 > The Bacterial Cell Wall and Beta-Lactam Antibiotics > Flashcards

The Bacterial Cell Wall and Beta-Lactam Antibiotics Flashcards

1
Q

Gram positive bacteria are ____ under a microscope (after staining)

A

Dark Purple

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2
Q

Gram negative bacteria are ____ under a microscope (after staining)

A

Light Pink

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3
Q

Describe a Gram positive cell wall

A

Peptidoglycan – lots of it Bacterial membrane underneath

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4
Q

Describe a Gram negative cell wall

A

Outer envelope w/Porins Periplasmic space Less peptidoglycan Bacterial membrane

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5
Q

Other name for Penicillin-binding proteins

A

Transpeptidases

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6
Q

Difference in drug penetrance between G+ and G- bacteria

A

In G+ –> Drugs can penetrate outer layers of the wall effectively, membrane is main protective layer In G- –> Outer membrane excludes drugs, but some can still get in through porins in the outer membrane

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7
Q

Difference in beta-lactamase secretions between G+ and G-

A

G+ –> excreted through the cell well to the external environment. Larger quantities produced G- –> Confined to periplasmic space

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8
Q

Which type of bacteria has a thicker peptidoglycan layer

A

G+

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9
Q

Which type of bacterial membrane is more lipoidal?

A

G-

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10
Q

In G- bacteria, the peptidoglycan contains a ______ residue. In G+ this residue is replaced by a ______ residue.

A

Meso-diaminopimelic acid residue (DAP) L-lysine residue (COOH of DAP replaced by an H)

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11
Q

Main components of peptidoglycan

A

N-acetylglucosamine and N-acetylmuramic acid

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12
Q

In G- cells, peptidoglycan is cross linked by…

A

Bridge between DAP residue of one stand and the terminal D-Ala of the other

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13
Q

In G+ cells, peptidoglycan is cross linked by…

A

L-Lys strand and the terminal D-Ala of the second molecule

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14
Q

The cross link between peptidoglycan molecules typically consists of ___ amino acids

A

5 Ex. S. aureus has 5 glycines

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15
Q

What happens in the transpeptidase reaction to connect S. aureus peptidoglycan

A

Since S. aureus is G+, The terminal glycine of one residue attaches to the penultimate Alanine residue, releasing the terminal D-Ala on the second molecule.

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16
Q

beta-Lactam mechanism of action?

A

Inhibition of transpeptidases that glue the peptidoglycan strands together by cross linking

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17
Q

beta-lactam antibiotics work by ______ the transpeptidase on the _____ residue

A

Acetylating Serine

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18
Q

Following beta-lactam exposure, the bacterial cell wall…

A

is subject to cell lysis and cell death

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19
Q

The beta-lactam system is very reactive due to steric strain. The NCC bond angle is a ____ angle, compared to the normal _____ angle.

A

90 degree 120 degree

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20
Q

Aside from steric strain, the beta-lactam carbonyl is also more reactive due to….

A

its poor stereoelectronics. These make it more like a ketone carbonyl than an aminde carbonyl due to the overlap on non-bonded electrons. In Bryan words – to make the Nitrogen’s electrons fit with the C=O, they have to fold up in a weird shape that inhibits their ability to have resonance. Makes it more ketone-like

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21
Q

Penicillins assume what structure

A

Folded ring with sp3 hybridized Nitrogen

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22
Q

Why don’t bacterial transpeptidases catalyze reactions with host cell proeins?

A

The bacterial substrate contain D-Ala amino acid residue not found in host cell proteins

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23
Q

Causes of beta-lactam resistance

A

Decreased cellular uptake of drug Mutation of Pen-binding proteins Presence of an Efflux pump Induction/Elaboration of bacterial beta-lactamases

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24
Q

What do beta-lactamases do?

A

Catalyze the hydrolysis of the beta-lactam moiety

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25
Q

Difference between the chemical reaction of a beta-lactam+transpeptidase and the reaction of a beta-lactam and beta-lactamase

A

Basically nothing except the beta-lactamases are recyclable

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26
Q

T or F. Resistance to beta-lactams is uncommon.

A

False. It is increasingly common

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27
Q

Describe the speed of the hydrolysis of the acetylated intermediate

A

Its fast, so the enzyme can hydrolyze many drug molecules rapidly

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28
Q

About ___% of the US population is allergic to beta-lactams

A

6-8

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29
Q

Cause of the allergenicity of beta-lactams

A

The drug acts as a hapten It acetylates host cell proteins, which then raise Abs

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30
Q

Why can’t the drug be modified to cause no allergic reaction

A

The site that causes the allergy is also the one that causes the antimicrobial fxn

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31
Q

Can a person who has demonstrated a penicillin allergy of one kind be given a different type of penicillin to avoid allergic response.

A

No. No they cannot.

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32
Q

Recommendations for patients that are unsure about allergy status?

A

Topical flare and wheal test for beta-lactam allergy

33
Q

Under acidic conditions (the stomach), the main degradation products of Pen G are…

A

BenzylpenicILLENIC Acid BenzylpenILLIC Acid BenzylpenicILLOIC Acid

34
Q

How is penicillenic acid made in acidic degradation.

A

Beta-elimination of sulfhydryl group in the second penicillin break down intermediate

35
Q

How much antibiotic activity is retained by penicillin hydrolysis products

A

No antibiotic activity

36
Q

T or F. Hydrolysis of the beta-lactam is irreversible.

A

True. Once the ring has been opened, it can’t be pushed back shut

37
Q

Significance of electronegative substituents on the side chain carbonyl. How does that work.

A

Electronegative substituents on the side chain carbonyl reduce the nucleophilicity of the side chain amide carbonyl oxygen atom. This stabilizes the penicillin against hydrolsis under acidic conditions and increased bioavailability.

38
Q

Give an example of a Penicillin made more stable by addition of an electronegative group

A

Penicillin G is 80% hydrolyzed in te stomach An extra Oxygen makes Penicillin V 35% hydrolyzed in the stomach.

39
Q

Storage and longevity of penicillin solutions.

A

They should be used promptly (if being used parenterally) Store in fridge btw pH 6-6.8

40
Q

_____ catalyze penicillin degradation reactions and should be kept away from solutions

A

Heavy metal ions

41
Q

What makes certain penicillins more able to bind serum proteins more effectively.

A

More lipophilic side chains

42
Q

Pro of serum protein binding

A

In general, it protects drugs from degradation

43
Q

Serum protein binding _____ the bioavailability. Why?

A

Reduces Reduces effective concentration of free drug.

44
Q

Why aren’t penicillin half lives altered by protein binding?

A

Their dissociation rates from the protein are fast and the renal excretion rates are rate limiting

45
Q

___% of penicillin renal excretion is performed by glomerular filtration. _____% by tubular secretion.

A

10% 90%

46
Q

Relationship of Probenecid and Penicillin

A

Porbenecid is an anion administered with penicillin that will compete with penicillin for secretion, increasing the half life of penicillin.

47
Q

Antimicrobial spectrum for Benzylpenicillin (Pen G)

A

G+ N. gonorrhoeae + H. influenza

48
Q

Is Benzylpenicillin (Pen G) sensitive to beta-lactamase?

A

yes

49
Q

How is Benzylpenicillin (Pen G) administered?

A

Orally in large doses (due to stomach acid) Most effective parenteral

50
Q

Toxicity associated with Benzylpenicillin (Pen G)?

A

Acute Allergic Reactions

51
Q

Precautions for Benzylpenicillin (Pen G)

A

Patients with significant allergy/asthma history

52
Q

Methicillin. Beta-lactamase sensitive?

A

No Steric hindrance of the nucleophilic attack by the enzyme on the beta-lactam carbonyl

53
Q

Removal of one Methicillin methoxyl group (or a change to para position) will cause…

A

Abolished beta-lactamase sensitivity

54
Q

How is Methicillin administered?

A

By injection Unstable to acid in the stomach due to electron donation toward the added o-methoxy groups

55
Q

Antimicrobial spectrum of Methicillin?

A

beta-lactamase producing S. aureus

56
Q

Why should Methicillin only be used when required

A

It induces beta-lactamase production, making other penicillins less effective

57
Q

How does MRSA avoid Methicillin?

A

Mutation in a transpeptidase Methicillin resistance gene (mecA) and Penicillin binding protein (PBP2)

58
Q

Cephapirin is what type of antibiotic

A

Cephalosporin

59
Q

What is fused to the beta lactam in Cephapirin

A

A six-membered sulfur containing ring (instead of the boring 5 member one)

60
Q

Cephalosporins with have an acetate in the 3-position are…

A

metabolically inactivated by hydrolysis by host esterases Makes hydroxymethyl acid that lactonizes

61
Q

What are carbapenems?

A

Carbon analogs of penicillins Sulfur group in thiazolide ring of penicillins becomes methylene

62
Q

Imipenem. beta lactamase sensitivity?

A

Reacts with an inhibits beta-lactamases

63
Q

Imipenem is hydrolyzed by…. How to get around it?

A

Renal dihydropeptidase-1 Cilastatin (a dihydropeptidase inhibitor)

64
Q

Perks of Imipenem + Cilastatin

A

Broader spectrum of antibiotic activity than anything else in US Gram + and Gram - “Magic Bullets”

65
Q

Why is Imipenem + Cilastatin restricted?

A

To avoid bacterial resistance

66
Q

Imipenem + Cilastatin is typically used to treat…

A

Serious gut infections, GU, Bone, Skin, and Endocardium

67
Q

Imipenem + Cilastatin route of administration

A

Parenterally

68
Q

Aztreonam is completely synthetic, but inspired by…

A

monocyclic beta-lactams (monobactams

69
Q

In Aztreonam, the C2 carboxyl group is replaced with

A

Sulfamic Acid

70
Q

Aztreonam antibiotic spectrum.

A

Almost entirely G-

71
Q

What makes Aztreonam so good anyway?

A

The Sulfamic Acid activates the beta-lactam ring toward hydrolysis and to rxn with penicillin binding proteins

72
Q

Indication for Aztreonam?

A

Severe G- Infections, especially with penicillin-resistant hospital organisms.

73
Q

Cross allergenicity with penicillins and cephalosporins…is it a thing?

A

No (except for Ceftazidime)

74
Q

Identify

A

Benzylpenicillin

75
Q

Identify.

A

Methicillin

76
Q

Identify.

A

Cephaprin

77
Q

Identify.

A

Imipenem

78
Q

Identify.

A

Aztreonam

Pharmacology -- Test #2 (13 decks)

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