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Questions and Answers
What is a primary cause of antibiotic resistance in penicillins?
What is a primary cause of antibiotic resistance in penicillins?
Which type of bacteria is resistant to ampicillin and amoxicillin without a β-lactamase inhibitor?
Which type of bacteria is resistant to ampicillin and amoxicillin without a β-lactamase inhibitor?
Which of the following adverse reactions is most prominent with penicillin use?
Which of the following adverse reactions is most prominent with penicillin use?
Which of these penicillin combinations is administered intravenously or intramuscularly?
Which of these penicillin combinations is administered intravenously or intramuscularly?
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Which condition may result from penicillin use due to its effect on intestinal flora?
Which condition may result from penicillin use due to its effect on intestinal flora?
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What is a notable characteristic of β-lactam antibiotics in terms of allergy?
What is a notable characteristic of β-lactam antibiotics in terms of allergy?
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What primarily initiates cell lysis in bacteria?
What primarily initiates cell lysis in bacteria?
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What type of bacteria are penicillins ineffective against?
What type of bacteria are penicillins ineffective against?
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What is the mechanism of action of penicillin?
What is the mechanism of action of penicillin?
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Which of the following natural penicillins is known for poor oral absorption?
Which of the following natural penicillins is known for poor oral absorption?
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Which of the following penicillins is considered β-lactamase-resistant?
Which of the following penicillins is considered β-lactamase-resistant?
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What condition can amoxicillin prevent during dental surgery?
What condition can amoxicillin prevent during dental surgery?
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What is the primary function of β-lactamase inhibitors like clavulanic acid?
What is the primary function of β-lactamase inhibitors like clavulanic acid?
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What are the short peptide chains associated with NAM subunits used for?
What are the short peptide chains associated with NAM subunits used for?
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What is a significant risk associated with methicillin use?
What is a significant risk associated with methicillin use?
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What bacterial structure does penicillin specifically target?
What bacterial structure does penicillin specifically target?
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Which pathogen is associated with vancomycin resistance?
Which pathogen is associated with vancomycin resistance?
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What do penicillins primarily interfere with regarding bacterial cells?
What do penicillins primarily interfere with regarding bacterial cells?
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Which of the following bacteria is recognized as a carbapenem-resistant organism?
Which of the following bacteria is recognized as a carbapenem-resistant organism?
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Which feature differentiates gram-negative bacteria from gram-positive bacteria?
Which feature differentiates gram-negative bacteria from gram-positive bacteria?
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Which antibiotic class is known as cell wall inhibitors?
Which antibiotic class is known as cell wall inhibitors?
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Which mechanism does Acinetobacter baumannii primarily use to escape antibiotic effects?
Which mechanism does Acinetobacter baumannii primarily use to escape antibiotic effects?
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What is the primary structure that penicillin-binding proteins (PBPs) cross-link?
What is the primary structure that penicillin-binding proteins (PBPs) cross-link?
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Which bacterial pathogen is known for multidrug resistance and is included in the ESKAPE pathogens?
Which bacterial pathogen is known for multidrug resistance and is included in the ESKAPE pathogens?
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What is a key characteristic of water-filled channels (porins) in gram-negative bacteria?
What is a key characteristic of water-filled channels (porins) in gram-negative bacteria?
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Study Notes
Cell Wall Inhibitors
- The cell wall of gram-positive bacteria is easily traversed by penicillin, while gram-negative bacteria have an outer lipopolysaccharide membrane that blocks these drugs.
- Penicillin-binding proteins (PBPs) are membrane proteins that cross-link peptidoglycan.
Mechanism of Action
- Penicillins interfere with cross-linking of the peptidoglycan cell wall, resulting in exposure of the osmotically less stable membrane.
- Cell lysis can occur via osmotic pressure or activation of autolysins.
- Penicillins are only effective against rapidly growing organisms that synthesize a peptidoglycan cell wall.
Bacterial Cell Wall
- The bacterial cell wall consists of repeating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) subunits.
- The NAM subunits have short peptide chains used in cross-linking.
- Penicillin-binding protein (PBP) forms a cross-link with another strand of the bacterial cell wall.
- The PBP dissociates from the wall once the cross-link has been formed.
- Penicillin can enter PBP active sites and react with the serine group.
- The beta-lactam ring of penicillin covalently linked to the PBP permanently blocks the PBP.
Antibacterial Spectrum
-
Natural Penicillins
- Penicillin G and penicillin V
- Susceptible to beta-lactamases.
- Penicillin V has poor oral absorption and is not indicated for bacteremia.
- More acid stable than penicillin G.
-
Antistaphylococcal Penicillins (β-lactamase-resistant penicillins)
- Methicillin, nafcillin, oxacillin, and dicloxacillin.
- Restricted to the treatment of infections caused by penicillinase-producing staphylococci, including methicillin-sensitive Staphylococcus aureus (MSSA).
- Methicillin is toxic (Interstitial nephritis) and is not clinically used anymore.
- No activity against gram-negative infections.
-
Extended-spectrum Penicillins (Semisynthetic penicillins)
- Ampicillin and amoxicillin.
- Similar antibacterial spectrum to penicillin G but are more effective against gram-negative bacilli.
- Treat respiratory infections.
- Amoxicillin prevents bacterial endocarditis during dental surgery.
- Protection from enzymatic hydrolysis by β-lactamase inhibitors (clavulanic acid/sulbactam).
- MRSA can be treated with vancomycin.
-
Antipseudomonal Penicillins
- Piperacillin and ticarcillin
- Effective towards many gram-negative bacilli, but not towards Klebsiella (contains penicillinase).
Resistance
- Inactivation of antibiotic by ß-lactamase (major cause)
- Modification of target PBPs
- Impaired penetration of the drug to target PBPs
- Efflux
Pharmacokinetics of Penicillins
- Administration:
- IV or IM: Ampicillin + sulbactam, ticarcillin + clavulanic acid, piperacillin + tazobactam, nafcillin, oxacillin.
- Oral: Penicillin V, amoxicillin, dicloxacillin
- IM (Depot forms): Procaine penicillin G, benzathine penicillin G - slowly absorbed into circulation and persist at low levels.
Adverse Reactions
- Hypersensitivity (most prominent) - ranging from rashes to angioedema and anaphylaxis.
- Cross-allergic reactions occur among the β-lactam antibiotics.
- Diarrhoea - disruption of the normal balance of intestinal flora.
- Pseudomembranous colitis from Clostridium difficile and other organisms may occur with penicillin use.
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Description
Test your knowledge on the mechanisms of action of cell wall inhibitors, particularly penicillins, and their effects on gram-positive and gram-negative bacteria. This quiz covers the structure of bacterial cell walls, the role of penicillin-binding proteins, and how these antibiotics function against bacterial infections.
