48 Questions
Which of the following bacteria produces penicillinases that degrade natural penicillins?
Bacteroides fragilis
What is a limitation of natural penicillins?
They are ineffective against bacteria with altered PBPs
Which of the following bacteria is susceptible to natural penicillins?
All of the above
What is the mechanism of resistance of methicillin-resistant S.aureus (MRSA) to antistaphylococcal penicillins?
Altered PBPs
What is the characteristic of antistaphylococcal penicillins?
They have bulky R side chains
Which of the following is NOT a limitation of natural penicillins?
Resistance to gram-negative bacteria
Which of the following bacteria is resistant to antistaphylococcal penicillins?
Methicillin-resistant S.aureus (MRSA)
What is the mechanism of action of antistaphylococcal penicillins?
Inhibition of cell wall synthesis
What is an important feature of extended-spectrum penicillins?
They are active against even more enteric gram-negative rods and P. aeruginosa
What is the effect of adding a β-lactamase inhibitor to an aminopenicillin?
It expands the spectrum of these agents to include many aerobic gram-negative bacilli and anaerobes
What is a characteristic of antistaphylococcal penicillins?
They are useful in treating infections caused by Staphylococcus
What is a difference between natural penicillins and aminopenicillins?
Aminopenicillins have improved activity against aerobic gram-negative bacilli
What is a characteristic of extended-spectrum penicillins?
They have improved activity against aerobic gram-negative bacilli, including P. aeruginosa
What is the result of using extended-spectrum penicillins in combination with β-lactamase inhibitors?
They are among the most powerful antibacterial agents available today
What is a feature of natural penicillins?
They have moderate activity against aerobic gram-positive bacteria and anaerobic bacteria
What is the mechanism of action of penicillins?
They bind to enzymes that function to assemble bacterial cell walls
What is the source of the first members of the cephalosporin class of antibiotics?
Fungus Cephalosporium acremonium
What is the categorization scheme used to organize cephalosporins?
By generation
What do cephalosporins have in common with penicillins?
Both are beta-lactam antibiotics
What is the common feature of the structure of cephalosporins?
Two side chains
What is the name of the fungus that was the source of the first members of the cephalosporin class of antibiotics?
Cephalosporium acremonium
What is the benefit of categorizing cephalosporins by generation?
Easier to remember the properties of the many cephalosporins
What is the name of the antibiotic class that cephalosporins belong to?
Beta-lactam
What is the common feature of cephalosporins and penicillins?
Both are beta-lactam antibiotics
What is the source of the first members of the cephalosporin class of antibiotics?
Cephalosporium acremonium
What do cephalosporins and penicillins have in common?
They are both beta-lactam antibiotics
What is the common feature of the structure of cephalosporins?
They have a nucleus with two side chains
What is the benefit of categorizing cephalosporins by generation?
It helps to predict their antibacterial spectrum
What is the name of the antibiotic class that cephalosporins belong to?
Beta-lactam antibiotics
What is the characteristic of cephalosporins that allows them to be categorized by generation?
Their antibacterial spectrum
What is the common feature of cephalosporins and penicillins?
They are both beta-lactam antibiotics
What is the categorization scheme used to organize cephalosporins?
By generation
What is the primary addition that extends the activity of extended-spectrum penicillins to include most enteric gram-negative bacilli?
A -lactamase inhibitor
Which type of bacteria are natural penicillins moderately active against?
Anaerobic bacteria
What is the primary mechanism of action of penicillins?
Binding to bacterial enzymes that assemble peptidoglycan
What is the primary advantage of aminopenicillins over natural penicillins?
Improved activity against aerobic gram-negative bacteria
Which bacteria do not make peptidoglycan and therefore are not affected by the natural penicillins?
Mycoplasma spp.
Which type of bacteria is P. aeruginosa?
Aerobic gram-negative bacteria
What is the main reason why some bacteria are resistant to natural penicillins?
They produce enzymes that break down penicillins.
Which bacteria remain susceptible to penicillin despite being gram-negative?
Neisseria meningitidis
What is the primary feature of extended-spectrum penicillins?
Activity against P. aeruginosa
What is the result of combining extended-spectrum penicillins with -lactamase inhibitors?
Activity against most aerobic gram-negative bacteria, aerobic gram-positive bacteria, and anaerobes
What is the characteristic of antistaphylococcal penicillins that makes them effective against staphylococcal infections?
They are resistant to beta-lactamases.
What is the primary function of the bacterial enzymes that penicillins bind to?
To assemble peptidoglycan
Which of the following bacteria is NOT affected by natural penicillins due to the production of penicillinases?
Streptococcus pneumoniae
What is the main difference between natural penicillins and antistaphylococcal penicillins?
Antistaphylococcal penicillins are resistant to beta-lactamases.
Which of the following bacteria is susceptible to natural penicillins despite being anaerobic?
Actinomyces israelii
What is the common feature of the bacteria that are susceptible to natural penicillins?
They all have a peptidoglycan layer in their cell walls.
Study Notes
Penicillins
- Act by binding to PBPs, which are bacterial enzymes that function to assemble peptidoglycan.
- Natural penicillins have moderate activity against aerobic gram-positive bacteria and anaerobic bacteria, but poor activity against aerobic gram-negative bacteria and most atypical bacteria.
- Limitations of natural penicillins include:
- Producing penicillinases that degrade natural penicillins (e.g., some anaerobes, such as Bacteroides fragilis).
- Some bacteria produce PBPs that do not bind natural penicillins with high affinity (e.g., some strains of Streptococcus pneumoniae).
- Some bacteria do not make peptidoglycan and are not affected by natural penicillins (e.g., Mycoplasma and Chlamydia spp.).
Antistaphylococcal Penicillins
- Have bulky residues on their R side chains that prevent binding by staphylococcal β-lactamases.
- Useful in treating infections caused by S. aureus and Staphylococcus epidermidis, but not effective against methicillin-resistant S. aureus (MRSA) and methicillin-resistant S. epidermidis (MRSE).
Extended-Spectrum Penicillins
- Active against even more enteric gram-negative rods and importantly, Pseudomonas aeruginosa.
- Addition of a β-lactamase inhibitor to an extended-spectrum penicillin extends its activity to include most enteric gram-negative bacilli.
Cephalosporins
- Constitute a large extended family of antibiotics within the β-lactam group.
- Can be categorized by "generation", with each generation having similar spectra of activity.
- Each cephalosporin is composed of a nucleus with two side chains.
Penicillins
- Act by binding to PBPs, which are bacterial enzymes that function to assemble peptidoglycan.
- Natural penicillins have moderate activity against aerobic gram-positive bacteria and anaerobic bacteria, but poor activity against aerobic gram-negative bacteria and most atypical bacteria.
- Limitations of natural penicillins include:
- Producing penicillinases that degrade natural penicillins (e.g., some anaerobes, such as Bacteroides fragilis).
- Some bacteria produce PBPs that do not bind natural penicillins with high affinity (e.g., some strains of Streptococcus pneumoniae).
- Some bacteria do not make peptidoglycan and are not affected by natural penicillins (e.g., Mycoplasma and Chlamydia spp.).
Antistaphylococcal Penicillins
- Have bulky residues on their R side chains that prevent binding by staphylococcal β-lactamases.
- Useful in treating infections caused by S. aureus and Staphylococcus epidermidis, but not effective against methicillin-resistant S. aureus (MRSA) and methicillin-resistant S. epidermidis (MRSE).
Extended-Spectrum Penicillins
- Active against even more enteric gram-negative rods and importantly, Pseudomonas aeruginosa.
- Addition of a β-lactamase inhibitor to an extended-spectrum penicillin extends its activity to include most enteric gram-negative bacilli.
Cephalosporins
- Constitute a large extended family of antibiotics within the β-lactam group.
- Can be categorized by "generation", with each generation having similar spectra of activity.
- Each cephalosporin is composed of a nucleus with two side chains.
Learn about the mechanism of action of penicillins, their activity against various bacteria, and their limitations. Understand how penicillinases and PBPs affect their efficacy.
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