40 Questions
Which of the following bacteria is susceptible to first-generation cephalosporins?
E. coli
What is the main difference between true cephalosporins and cephamycins?
The fungus they were originally isolated from
Why are first-generation cephalosporins ineffective against MRSA and MRSE?
Because they are incapable of binding to their PBPs
What is the main limitation of first-generation cephalosporins against gram-negative bacteria?
Their inability to protect against -lactamases of gram-negative bacteria
Which of the following bacteria is not susceptible to first-generation cephalosporins?
L. monocytogenes
What is the main advantage of second-generation cephalosporins over first-generation cephalosporins?
Their increased ability to protect against -lactamases of gram-negative bacteria
What is the activity of true cephalosporins against Gram-positive bacteria?
Equivalent to first-generation agents
Which of the following is not a Gram-negative bacterium that is susceptible to second-generation cephalosporins?
Staphylococcus aureus
What is the anaerobic activity of cefoxitin and cefotetan?
Moderate anaerobic activity
Which generation of cephalosporins has activity against anaerobic bacteria?
Second-generation cephalosporins
What is the activity of cefoxitin and cefotetan against Gram-positive bacteria?
Little activity
Which of the following bacteria is susceptible to second-generation cephalosporins?
Klebsiella pneumoniae
What is the activity of true cephalosporins against Gram-negative bacteria?
Equivalent to first-generation agents
Which of the following is a characteristic of second-generation cephalosporins?
Moderate anaerobic activity
What is the difference in activity against aerobic gram-positive bacteria between individual second-generation cephalosporins?
The cephamycins have relatively limited activity
What is the strength of the second-generation cephalosporin agents?
Their increased activity against aerobic and facultative gram-negative bacteria
Which bacteria are the true cephalosporins also active against?
Neisseria spp. and H. influenzae
What is the consequence of the additional methoxy group on the β-lactam ring of the cephamycins?
Enhanced stability to the β-lactamases of some anaerobes
What is the trade-off for the cephamycins' enhanced anaerobic activity?
Decreased activity against staphylococci and streptococci
Why are agents like cefotetan and cefoxitin categorized as cephalosporins?
They are chemically and pharmacologically similar to cephalosporins
What is the primary limitation of first-generation cephalosporins against Staphylococcus aureus?
Lack of activity against MRSA and MRSE
Which of the following bacteria is susceptible to first-generation cephalosporins?
E.coli
What is the difference between true cephalosporins and cephamycins?
Cephamycins are derivatives of Streptomyces lactamdurans
What is the main advantage of second-generation cephalosporins over first-generation cephalosporins?
Improved activity against gram-negative bacteria
What is the primary activity of cefoxitin and cefotetan?
High activity against anaerobes
What is the primary advantage of cephamycins over true cephalosporins?
Enhanced activity against anaerobes
What is a common characteristic of second-generation cephalosporins?
Increased activity against aerobic and facultative gram-negative bacteria
Which of the following bacteria is not affected by the additional methoxy group on the β-lactam ring of the cephamycins?
B. fragilis
What is the main difference in activity between true cephalosporins and cephamycins against aerobic gram-positive bacteria?
Cephamycins have relatively limited activity
Which of the following is a characteristic of the cephamycins?
Enhanced stability to the β-lactamases of some anaerobes
Why are agents like cefotetan and cefoxitin categorized as cephalosporins?
They have similar pharmacological activity to cephalosporins
What is the consequence of the additional methoxy group on the β-lactam ring of the cephamycins?
Decreased activity against aerobic gram-positive bacteria
What is the key difference in the nucleus of cephalosporins compared to penicillin?
The -lactam ring is fused to a six-member dihydrothiazine ring
What is one advantage of the cephalosporin core over the penicillin core?
It is more resistant to cleavage by -lactamases
What is the site of attachment for cephalosporins that exerts their antibiotic effect?
PBP receptors
What are the two sites on the cephalosporin core that can be modified?
R1 and R2
What is the ring structure fused to the -lactam ring in cephalosporins?
Six-member dihydrothiazine ring
What is the mechanism of action of cephalosporins?
Inhibiting peptidoglycan synthesis
What is a key advantage of cephalosporins over penicillin?
They have two sites, R1 and R2, that can be modified
What is the structural feature of cephalosporins that allows them to be more resistant to -lactamases?
The -lactam ring is fused to a six-member dihydrothiazine ring
Study Notes
First-Generation Cephalosporins
- Effective against infections caused by many strains of Staphylococcus aureus
- Ineffective against MRSA, MRSE, and highly penicillin-resistant Streptococcus pneumoniae
- Limited activity against aerobic and facultative gram-negative bacteria
- Susceptible to some strains of E. coli, Klebsiella pneumoniae, and Proteus mirabilis
- Moderate to poor activity against anaerobes, intracellular bacteria, and spirochetes
Second-Generation Cephalosporins
- Divided into two groups: true cephalosporins (e.g. cefuroxime) and cephamycins (e.g. cefotetan and cefoxitin)
- Cephamycins are derivatives of a parent compound from Streptomyces lactamdurans
- True cephalosporins have activity equivalent to first-generation agents against gram-positive bacteria
- Cephamycins have little activity against gram-positive bacteria
- Active against gram-negative bacteria, including Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Haemophilus influenzae, and Neisseria spp.
- Cefoxitin and cefotetan have moderate anaerobic activity
Cephamycins
- Include cefotetan and cefoxitin
- Have relatively limited activity against aerobic gram-positive bacteria
- Have enhanced stability to the β-lactamases of some anaerobes, such as B. fragilis
- Diminished activity against staphylococci and streptococci due to decreased affinity for the PBPs of these bacteria
Second-Generation Cephalosporins
- Not actually cephalosporins, but chemically and pharmacologically similar
- Differ in activity against aerobic gram-positive bacteria
- True cephalosporins are as active against aerobic gram-positive cocci as first-generation agents
- Cephamycins (cefotetan and cefoxitin) have relatively limited activity against these bacteria
Activity Against Bacteria
- Second-generation agents have increased activity against:
- Aerobic and facultative gram-negative bacteria
- E. coli, K. pneumoniae, and P. mirabilis
- Neisseria spp.
- H. influenzae (including β-lactamase-producing strains)
- Cephamycins have enhanced stability against β-lactamases of some anaerobes (e.g., B. fragilis)
- True cephalosporins are more active against H. influenzae and Neisseria spp.
Comparison with First-Generation Cephalosporins
- First-generation cephalosporins have limited activity against:
- Aerobic and facultative gram-negative bacteria
- Anaerobes, intracellular bacteria, and spirochetes
- First-generation cephalosporins are ineffective against:
- MRSA and MRSE
- Many highly penicillin-resistant S. pneumoniae
- L. monocytogenes and enterococci
Structure and Mechanism of Action
- Cephalosporin nucleus is 7-aminocephalosporanic acid
- β-Lactam ring is fused to a six-member dihydrothiazine ring
- Cephalosporin core has two major advantages over penicillin core:
- Intrinsic resistance to cleavage by β-lactamases
- Two sites (R1 and R2) for modification
- Cephalosporins exert their effects by attaching to and inhibiting PBPs, preventing peptidoglycan synthesis
Learn about the effectiveness of cephalosporin antibiotics against various bacterial strains, including Staphylococcus aureus, MRSA, and Streptococcus pneumoniae.
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