Penicillins and Cephalosporins

Question 1

What protects bacteria from membrane rupture?

Answer 1

A highly cross-linked cell wall

Question 2

What does penicillin inhibit in bacterial cell walls?

Answer 2

Cross-linking of cell wall units

Question 3

What happens when penicillin disrupts cross-linking in the cell wall?

Answer 3

Autolysins create weak points, causing membrane extrusion and rupture

Question 4

What is the result of bacterial membrane rupture?

Answer 4

Bactericidal action

Question 5

Is penicillin effective against resting or actively dividing cells?

Answer 5

Effective against rapidly dividing cells; relatively inactive against resting cells

Question 6

What is the first stage of bacterial cell wall synthesis?

Answer 6

Production of cell wall building blocks (UDP-acetyl-muramyl-pentapeptide) inside the cell

Question 7

Which drug inhibits the first stage of cell wall synthesis?

Answer 7

Cycloserine

Question 8

What occurs in the second stage of cell wall synthesis?

Answer 8

Precursor is carried across the membrane; formation of linear peptidoglycan and linkage to existing wall

Question 9

Which drug inhibits the second stage of cell wall synthesis?

Answer 9

Bacitracin

Question 10

What is the third stage of bacterial cell wall synthesis?

Answer 10

Cross-linking of the cell wall

Question 11

Which antibiotics inhibit the cross-linking stage?

Answer 11

Penicillin, cephalosporins, and vancomycin

Question 12

What is the target site of action for penicillin and cephalosporins?

Answer 12

The transpeptidase enzyme involved in cross-linking

Question 13

Why can penicillin bind to the transpeptidase enzyme?

Answer 13

Its structure mimics the D-alanyl-D-alanyl terminus of the peptidoglycan side chain

Question 14

How does penicillin inhibit transpeptidase?

Answer 14

It occupies the D-ala-D-ala substrate site and forms a covalent bond with the enzyme

Question 15

Why are some gram-negative bacteria resistant to penicillin?

Answer 15

Due to lack of accessibility to the target site

Question 16

What enzymes do bacteria produce to inactivate penicillin?

Answer 16

Penicillinases (or beta-lactamases)

Question 17

How can penicillin binding proteins (PBPs) contribute to resistance?

Answer 17

Through structural alterations in PBPs

Question 18

How does a change in PBP affinity affect penicillin effectiveness?

Answer 18

It reduces penicillin’s ability to bind and inhibit the enzyme

Question 19

How does increasing the amount of PBPs contribute to resistance?

Answer 19

By overwhelming the antibiotic, reducing its effectiveness

Question 20

What determines the effects of penicillin on a specific bacterium?

Answer 20

The types of PBPs that penicillin binds to

Question 21

What is the effect of penicillin binding to PBPs 2 and 3?

Answer 21

It prevents cell division and causes loss of rod shape (filament formation)

Question 22

What is the effect of penicillin binding to PBP 1?

Answer 22

It inhibits cell wall synthesis, leading to osmotic lysis

Question 23

How can changes in PBP affinity affect penicillin sensitivity?

Answer 23

Altered affinity can reduce penicillin effectiveness

Question 24

Is penicillin widely distributed in the body?

Answer 24

Yes, but with limitations

Question 25

Does penicillin cross the blood-brain barrier easily?

Answer 25

No, it does not readily enter the central nervous system

Question 26

Does penicillin reach joints or ocular tissues effectively?

Answer 26

No, it does not reach those tissues well

Question 27

What portion of a penicillin dose is excreted?

Answer 27

Approximately two-thirds

Question 27

What portion of a penicillin dose is metabolized?

Answer 27

Approximately one-third

Question 28

What serious immune reaction can penicillin cause?

Answer 28

Hypersensitivity or anaphylactic shock

Question 28

What type of neurological effects can penicillin cause?

Answer 28

Central nervous system effects

Question 28

What type of secondary infection can result from penicillin use?

Answer 28

Superinfection

Question 29

How is penicillin generally regarded in terms of toxicity?

Answer 29

It is considered relatively nontoxic

Question 30

What are cephalosporins derived from?

Answer 30

A fungus found in sewers

Question 31

Are cephalosporins resistant to penicillinase?

Answer 31

Yes

Question 32

How do cephalosporins act in comparison to penicillins?

Answer 32

They act similarly and have a similar structure

Question 32

What types of bacteria are cephalosporins effective against?

Answer 32

Many gram-positive and gram-negative organisms

Question 33

Can any cephalosporins be given orally?

Answer 33

Yes, such as cephalexin and cefaclor

Question 34

How are most cephalosporins administered?

Answer 34

By intravenous or intramuscular routes

Question 35

How well are cephalosporins distributed in the body?

Answer 35

They are well distributed, but with limited central nervous system penetration

Question 35

How are cephalosporins primarily excreted?

Answer 35

By the kidneys

Question 35

How are cephalothin and cefotaxime metabolized in the body?

Answer 35

They undergo deacylation to less potent metabolites

Question 36

Which cephalosporins can penetrate the cerebrospinal fluid?

Answer 36

Cefotaxime and ceftizoxime

Question 37

Do most cephalosporins undergo significant metabolism?

Answer 37

No, most undergo minimal metabolism

Question 38

How can bacterial proteins contribute to cephalosporin resistance?

Answer 38

Alteration in antibiotic binding proteins

Question 38

What can block renal excretion of cephalosporins?

Answer 38

Probenecid or renal failure

Question 39

What can prevent cephalosporins from working effectively?

Answer 39

Inability of the drug to reach its site of action

Question 39

How are cephalosporins used in surgical settings?

Answer 39

For prophylaxis during and after surgery, including for staphylococcal endocarditis

Question 40

When are cephalosporins especially useful?

Answer 40

For gram-negative infections, especially when organisms are penicillin-resistant

Question 41

What types of infections can cephalosporins treat?

Answer 41

Meningitis, streptococcal infections, and staphylococcal infections

Question 42

What enzyme can inactivate cephalosporins?

Answer 42

Cephalosporinase

Question 43

What type of antibiotic is vancomycin?

Answer 43

A large glycopeptide with a molecular weight of about 1500

Question 43

Which resistant gram-negative bacteria may produce cephalosporinase?

Answer 43

Pseudomonas and Proteus

Question 44

What is vancomycin’s mechanism of action?

Answer 44

It binds to the terminal D-ala-D-ala of the cell wall polymer, preventing synthesis of the long polymer backbone

Question 44

What infection is oral vancomycin used to treat?

Answer 44

Clostridioides difficile (C. difficile)

Question 44

What is vancomycin commonly used to treat?

Answer 44

Methicillin-resistant Staphylococcus aureus (MRSA) infections

Question 45

When is vancomycin typically used?

Answer 45

For serious, life-threatening gram-positive infections unresponsive to other antibiotics

Question 46

Why is vancomycin ineffective against gram-negative bacteria?

Answer 46

It generally cannot cross the outer membrane

Question 47

What are the routes of vancomycin administration?

Answer 47

Intravenous and oral (IV/PO)

Question 47

Does vancomycin have good systemic absorption when taken orally?

Answer 47

No, it has no systemic absorption

Question 48

What serious infection risk increases when vancomycin is combined with aminoglycosides?

Answer 48

Endocarditis

Question 48

How is vancomycin excreted?

Answer 48

By the kidneys

Question 48

What toxicities can occur if renal excretion of vancomycin is impaired?

Answer 48

Ototoxicity, nephrotoxicity, peripheral vasodilation, thrombocytopenia, and bleeding

Question 49

What is the key resistance mechanism against vancomycin?

Answer 49

Alteration of D-alanine-D-alanine to D-alanine-D-serine

Question 49

What is the clinical use of bacitracin?

Answer 49

Topical treatment of gram-positive skin and eye infections

Question 50

What is the mechanism of action of bacitracin?

Answer 50

It inhibits cell wall synthesis

Question 51

What class of antibiotic are carbapenems?

Answer 51

Beta-lactam antibiotics

Question 51

What is bacitracin often combined with in topical treatments?

Answer 51

Polymyxins or neomycin

Question 52

Why is bacitracin not used systemically?

Answer 52

It is too toxic for systemic use

Question 53

What is the mechanism of action of carbapenems?

Answer 53

They block cell wall synthesis by binding to PBPs and preventing cross-linking of the peptidoglycan backbone

Question 54

When are carbapenems typically used?

Answer 54

In cases of resistance to cephalosporins due to extended-spectrum beta-lactamases (ESBL)

Question 54

What are the key resistance mechanisms against carbapenems?

Answer 54

Production of carbapenem-destroying beta-lactamases, loss of permeability, and increased drug efflux

Question 54

What is the spectrum of activity of carbapenems?

Answer 54

Very broad; active against both gram-positive and gram-negative bacteria

Question 55

What makes carbapenems unique in treating ESBL-producing bacteria?

Answer 55

They are the sole antibiotic effective when bacteria are resistant to amoxicillin/clavulanate or piperacillin/tazobactam

Question 56

What serious infection are carbapenems used to treat, especially after prolonged cephalosporin or fluoroquinolone use?

Answer 56

Clostridioides difficile (C. difficile) infection

Question 57

How are carbapenems administered?

Answer 57

Intravenously (not orally)