Textbook Question
The use-dilution values for two disinfectants tested under the same conditions are as follows:
Disinfectant A—1:2
Disinfectant B—1:10,000.
If both disinfectants are designed for the same purpose, which would you select?
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11. Controlling Microbial Growth
Review of Chemicals Used to Control Microbial Growth
1:41 minutesProblem 9
Textbook Question
Compare the method of action of the following pairs:
a. Penicillin and echinocandin
b. Imidazole and polymyxin B
Verified step by step guidance1
Step 1: Understand the target of each drug class. Penicillin is a beta-lactam antibiotic that targets bacterial cell wall synthesis by inhibiting the enzyme transpeptidase, which is essential for cross-linking peptidoglycan layers. Echinocandins, on the other hand, inhibit fungal cell wall synthesis by blocking the enzyme 1,3-\(\beta\)-D-glucan synthase, which is crucial for producing glucan, a key component of fungal cell walls.
Step 2: Compare the mechanism of action of penicillin and echinocandin. Both interfere with cell wall synthesis but in different organisms and by targeting different enzymes and cell wall components—penicillin acts on bacteria by disrupting peptidoglycan cross-linking, while echinocandins act on fungi by inhibiting glucan synthesis.
Step 3: Understand the target and mechanism of imidazoles. Imidazoles are antifungal agents that inhibit the enzyme lanosterol 14-\(\alpha\)-demethylase, which is involved in ergosterol synthesis, an essential component of fungal cell membranes. This disruption leads to increased membrane permeability and fungal cell death.
Step 4: Understand the mechanism of polymyxin B. Polymyxin B is an antibiotic that targets Gram-negative bacteria by interacting with the lipopolysaccharides (LPS) and phospholipids in the outer membrane, disrupting membrane integrity and causing leakage of cellular contents.
Step 5: Compare imidazole and polymyxin B. Imidazoles disrupt fungal cell membrane synthesis by inhibiting ergosterol production, whereas polymyxin B directly disrupts bacterial outer membranes by binding to LPS and phospholipids, leading to membrane destabilization and cell death.
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Video duration:
1mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Mechanism of Action of Penicillin
Penicillin is a beta-lactam antibiotic that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs). This prevents the cross-linking of peptidoglycan chains, weakening the cell wall and causing bacterial lysis, especially in Gram-positive bacteria.
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Mechanism of Action of Echinocandin
Echinocandins are antifungal agents that inhibit the enzyme beta-(1,3)-D-glucan synthase, essential for synthesizing glucan polymers in the fungal cell wall. This disruption weakens the fungal cell wall, leading to osmotic instability and cell death, primarily targeting Candida and Aspergillus species.
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Mechanism of Action of Imidazole and Polymyxin B
Imidazoles are antifungal drugs that inhibit ergosterol synthesis, disrupting fungal cell membrane integrity. Polymyxin B is an antibiotic that binds to lipopolysaccharides in Gram-negative bacterial membranes, disrupting membrane permeability and causing leakage of cellular contents, leading to cell death.
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