Bacterial Cell Wall and Beta Lactam Antibiotics

Question 1

Color of gram (+) bacteria under gram stain?

Answer 1

dark purple

Question 2

Color of gram (-) bacteria under gram stain?

Answer 2

light pink

Question 3

How do gram (+) and gram (-) bacteria differ?

Answer 3

differ in the structures of their cell walls

Question 4

How can some drugs get into gram (-) bacteria?

Answer 4

through the porins in the outer membrane

Question 5

Is the peptidoglycan layer thicker in gram (-) or gram (+) bacteria?

Answer 5

much thicker in gram (+) bacteria

Question 6

How many membranes do gram (+) bacteria have?

Answer 6

one membrane

Question 7

How many membranes do gram (-) bacteria have?

Answer 7

two membranes - inner and an outer membrane

Question 8

What enzyme cross-links the peptidoglycan strands?

Answer 8

transpeptidase

Question 9

Describe the beta-lactam antibiotic mechanism of action.

Answer 9

inhibition of transpeptidases that “glue” the peptidoglycan strands together by cross-linking

Question 10

Why do the bacterial transpeptidases not catalyze reactions with host cell proteins?

Answer 10

the bacterial substrate contains unnatural D-Ala amino acid residues that are not found in the host cell proteins

Question 11

Name three ways resistance to beta-lactam antibiotics can develop.

Answer 11

1. decreased cellular uptake of the drug
2. mutation of the penicillin-bindin gproteins to decrease their affinity for penicillins
3. the presence of an efflux pump that pumps the antibiotic out of the cell

Question 12

Most common mechanism of resistance to beta-lactam antibiotics

Answer 12

induction or elaboration of bacterial beta-lactamases

Question 13

Describe the reaction that beta-lactamaes catalyze.

Answer 13

the hydrolysis of the beta-lactam moiety

Question 14

The allergenicity of beta-lactam antibiotics results from?

Answer 14

the drug acting as a hapten, acylates host cell proteins, which raise antibodies and cause an allergic reaction

Question 15

Can a person who has demonstrated an allergy to one penicillin be given another penicillin?

Answer 15

No, because cross-sensitivity is common.

Question 16

What should be kept away from penicillin solutions?

Answer 16

heavy metal ions (they catalyze penicillin degradation reactions)

Question 17

Which routes are penicillins rapidly excreted by?

Answer 17

the renal or biliary routes

Question 18

10% of renal excretion of penicillins is by?

Answer 18

glomerular filtration

Question 19

90% of renal excretion of penicillins is by?

Answer 19

tubular secretion

Question 20

What happens when probenecid is administered along with penicillin?

Answer 20

The anionic penicillin competes with the anion probenecid for the tubular secretion mechanism in the kidneys - causes an increase in the half life of penicillin

Question 21

Benzylpenicillin (Penicillin G) antimicrobial spectrum:

Answer 21

Gram (+) cocci + Neisseria gonorrhoeae and Haemophilus influenza [both gram (-)]

Question 22

Is Benzylpenicillin (Penicillin G) beta-lactamase sensitive?

Answer 22

yes

Question 23

Precautions when using Penicillin G (Benzylpenicillin)

Answer 23

Pen G should be used with caution in individuals with histories of significant allergies and/or asthma

Question 24

What drug is the drug of choice for treatment of more infections than any other antibiotic?

Answer 24

Pen G

Question 25

Is Methicillin beta-lactamase sensitive?

Answer 25

No.

Question 26

Why must methicillin be administered by injection?

Answer 26

it is unstable to acid in the stomach

Question 27

What’s the antibiotic spectrum of methicillin?

Answer 27

narrow. It is primarily for treatment of beta-lactamase-producing Staphylococcus aureus

Question 28

Why is MRSA resistant to Methacillin?

Answer 28

because of a mutation in the penicillin-binding protein (transpeptidase) - methicillin resistance gene (mecA)

Question 29

What kind of antibiotic is Cephapirin?

Answer 29

a cephalosporin antibiotic

Question 30

What does cepharpirin have fused to the beta-lactam instead of a five-membered ring?

Answer 30

It has a six-membered sulfur-containing ring fused to the beta-lactam

Question 31

Cephalosporins that have what are inactivated by the hydrolysis of the acetate by host esterases?

Answer 31

cephalosporins that have an acetate in the 3-position

Question 32

Carbapenems are carbon analogs of what?

Answer 32

penicillins

Question 33

Besides reacting with penicillin-binding proteins, what else does imipenem react with?

Answer 33

Imipenem reacts with and inhibits beta-lactamases

Question 34

What is imipenem hydrolyzed by?

Answer 34

renal dehydropeptidase-1

Question 35

How can you overcome the hydrolyzation of impenem by renal dehydropeptidase-1?

Answer 35

co-administration of the dehydropeptidase-1 inhibitor, cilastatin

Question 36

cilastatin

Answer 36

renal dehydropeptidase-1 inhibitor

Question 37

What has a broader spectrum of Abx activity than any other antibiotic presently available in the US?

Answer 37

the combination of imipenem with cilastatin

Question 38

What is imipenem with cilastatin active against?

Answer 38

gram (+) and gram (-) bacteria

Question 39

Why is imipenem use typically restricted?

Answer 39

to avoid widespread bacterial resistance

Question 40

What is the combination of imipenem with cilastatin used to treat?

Answer 40

serious infections of the gut, GU tract, bone, skin and endocardium

Question 41

Antibiotic spectrum on Aztreonam?

Answer 41

focuses almost completely on Gram (-) bacteria

Question 42

Aztreonam disodium is used mainly in the treatment of what?

Answer 42

severe infections with gram (-) bacteria, especially those by penicillin-resistant organisms acquired in hospitals

Question 43

Cross allergenicity with penicillins and cephalosporins has not been reported except for?

Answer 43

ceftazidimine - has an identical sidechain