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Questions and Answers
What is the minimum inhibitory concentration (MIC) of an antimicrobial agent?
What is the minimum inhibitory concentration (MIC) of an antimicrobial agent?
How do most bactericidal agents differ from bacteriostatic agents in terms of MIC and MBC?
How do most bactericidal agents differ from bacteriostatic agents in terms of MIC and MBC?
What is the reason behind the resistance developed against penicillins in bacteria?
What is the reason behind the resistance developed against penicillins in bacteria?
Which penicillin is effective against streptococci and Neisseria spp?
Which penicillin is effective against streptococci and Neisseria spp?
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Why is phenoxymethylpenicillin given orally instead of by injection?
Why is phenoxymethylpenicillin given orally instead of by injection?
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What is the significance of clavulanic acid in combination with amoxicillin?
What is the significance of clavulanic acid in combination with amoxicillin?
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What is the main structural difference between human cells and bacterial cells that antimicrobial agents exploit?
What is the main structural difference between human cells and bacterial cells that antimicrobial agents exploit?
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Which type of bacteria have a poorly-defined cell wall and do not retain the Gram stain?
Which type of bacteria have a poorly-defined cell wall and do not retain the Gram stain?
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What is the main component of bacterial cell walls that is essential for their survival?
What is the main component of bacterial cell walls that is essential for their survival?
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Which classification is based on the structural characteristics of bacterial cell walls?
Which classification is based on the structural characteristics of bacterial cell walls?
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What can be used to classify bacteria into two types based on their cell wall characteristics?
What can be used to classify bacteria into two types based on their cell wall characteristics?
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Which type of bacteria can be classified into groups like Gram-positive bacilli and Gram-negative cocci?
Which type of bacteria can be classified into groups like Gram-positive bacilli and Gram-negative cocci?
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Study Notes
Antimicrobial Agents
- Antibacterial agents exploit the differences between human and bacterial cells.
- Bacterial cells are prokaryotes, lack a membrane-bound nucleus, and can grow and divide rapidly.
- Bacterial cell walls are made of peptidoglycan and are essential for survival.
Classification of Bacteria
- The Gram stain characterizes bacteria based on cell wall structural characteristics.
- Bacteria can be classified into two types: Gram-positive and Gram-negative.
- Gram-positive bacteria include cocci and bacilli.
- Gram-negative bacteria include cocci and bacilli.
- Atypical bacteria (e.g., Chlamydia, Mycoplasma, Legionella) have a poorly-defined cell wall and do not hold the Gram stain.
Measures of Antimicrobial Susceptibility
- Minimum Inhibitory Concentration (MIC): the lowest concentration of an antimicrobial that inhibits visible growth of a micro-organism.
- Minimum Bactericidal Concentration (MBC): the minimum concentration of an antimicrobial agent needed to kill 99.9% of the original inoculum.
- Bactericidal agents have MICs and MBCs that are the same or only a few dilutions apart.
- Bacteriostatic agents have MBCs that are many dilutions higher than the MIC.
Cell Wall Active Agents: Penicillins
- Penicillins are used mainly to treat Gram-positive bacterial infections.
- Resistance is usually due to beta-lactamases produced by bacteria, which destroy the beta-lactam ring.
- Penicillins are poorly lipid soluble, resulting in poor penetration into the cerebrospinal fluid.
- Penicillins require dose reduction in severe renal failure.
- Benzylpenicillin is active against streptococci and Neisseria spp.
- Most staphylococci are resistant to benzylpenicillin due to penicillinases production.
- Phenoxymethylpenicillin is gastric acid-stable and can be given orally.
- Amoxicillin and ampicillin have a similar spectrum of activity, but are inactivated by beta-lactamase.
- Ampicillin is rarely used, replaced by Amoxicillin with better absorption properties.
- Amoxicillin can be given in combination with the beta-lactamase inhibitor clavulanic acid (co-amoxiclav).
- Flucloxacillin is not inactivated by beta-lactamase and is effective against beta-lactamase producing staphylococci.
- Antipseudomonal penicillins (piperacillin and ticarcillin) are only available in combination with beta-lactamase inhibitors.
- Temocillin is a beta-lactamase-resistant penicillin used to treat multi-drug resistant Gram-negative bacteria.
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Description
Test your knowledge on antimicrobial agents by learning about the differences between human and bacterial cells, sites of action for antimicrobial agents, MIC and MBC measures, and common issues with antimicrobial classes. This quiz will help you understand the key concepts of antimicrobial susceptibility.
