MICI: Antibiotics Pt 2

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Questions and Answers

What is the primary mechanism of action for fluoroquinolones like Ciprofloxacin?

Inhibition of protein synthesis at ribosomal subunits

Disruption of the bacterial cell wall

Inhibition of RNA synthesis

Inhibition of DNA gyrase and topoisomerase IV (correct)

Which of the following mechanisms contributes to antibiotic resistance through enzymatic degradation?

Target modification

Gene transfer via conjugation

Enzyme production like beta-lactamase (correct)

Efflux pump activity

Why are Gram-negative bacteria often more resistant to antibiotics than Gram-positive bacteria?

They lack peptidoglycan in their cell walls

They produce more efflux pumps (correct)

They do not possess ribosomes

They have a thicker peptidoglycan layer

What is the primary reason for monitoring blood levels of Vancomycin in patients?

To avoid nephrotoxicity and ototoxicity due to its narrow therapeutic window Signup and view all the answers

Which class of antibiotics acts as a competitive inhibitor of dihydropteroate synthase?

Sulfonamides Signup and view all the answers

What is a common clinical use for Rifampin?

Eradication of tuberculosis Signup and view all the answers

What structural difference in bacteria contributes to their susceptibility to different antibiotics?

Thickness of the peptidoglycan layer Signup and view all the answers

Which of the following antibiotics is commonly used for patients with a penicillin allergy?

Erythromycin Signup and view all the answers

Which mechanism allows bacteria to acquire resistance genes from other bacteria?

Horizontal gene transfer via transformation, transduction, or conjugation Signup and view all the answers

What is the primary target of aminoglycosides in bacterial cells?

Bacterial ribosomes Signup and view all the answers

What is the primary mechanism by which beta-lactam antibiotics work?

Prevent the cross-linking of NAM subunits in the peptidoglycan layer. Signup and view all the answers

Which of the following resistance mechanisms can render beta-lactam antibiotics ineffective?

Production of beta-lactamase enzymes that break down the beta-lactam ring. Signup and view all the answers

What is the mechanism of action of aminoglycosides like streptomycin?

Bind to the 30S subunit causing misreading of mRNA. Signup and view all the answers

What adverse effect is commonly associated with tetracyclines?

Tooth discoloration and skeletal growth inhibition. Signup and view all the answers

Which antibiotic binds to D-alanine-D-alanine terminus in peptidoglycan precursors?

Vancomycin. Signup and view all the answers

What is a known effect of the resistance mechanism involving substitution of D-alanine with D-lactate?

Prevention of vancomycin from binding to its target. Signup and view all the answers

Which antibiotic primarily inhibits protein synthesis by binding to the 50S ribosomal subunit?

Macrolides. Signup and view all the answers

Bacitracin works by preventing what process in bacterial cell function?

Transport of peptidoglycan precursors from cytoplasm to cell wall. Signup and view all the answers

Which class of antibiotics is known for causing resistance due to enzymatic modifications that inactivate them?

Aminoglycosides. Signup and view all the answers

How do glycopeptide antibiotics, such as vancomycin, achieve their antibacterial effect?

By blocking the cross-linking of peptidoglycan in the cell wall. Signup and view all the answers

Study Notes

Overview of Antibiotics Mechanisms of Action (MOA)

Antibiotics are categorized based on their mechanisms of action targeting essential bacterial processes.

Inhibition of Cell Wall Synthesis

Beta-lactams (e.g., Penicillin, Methicillin):
- Prevent cross-linking of NAM subunits in peptidoglycan layer.
- Disrupt cell wall synthesis by binding to penicillin-binding proteins (PBPs).
- Resistance: Many bacteria produce beta-lactamase enzymes that break down the antibiotic.
- Solutions include combination therapies like Piperacillin-Tazobactam with beta-lactamase inhibitors.
Vancomycin:
- Targets Gram-positive bacteria by binding to D-alanine-D-alanine termini in peptidoglycan precursors.
- Resistance arises when bacteria substitute D-alanine with D-lactate.
Glycopeptides and Bacitracin:
- Glycopeptides (e.g., Vancomycin) inhibit cross-linking in Gram-positive bacteria.
- Bacitracin intervenes in the transport of peptidoglycan precursors from cytoplasm to cell wall.

Inhibition of Protein Synthesis

Aminoglycosides (e.g., Streptomycin):
- Bind to the 30S ribosomal subunit, causing misreading of mRNA.
- Resistance through enzymatic modification by bacteria.
Tetracyclines:
- Attach to the 30S subunit, blocking tRNA attachment, thus halting protein synthesis.
- Adverse effects include tooth discoloration and skeletal growth inhibition; contraindicated in young children and pregnant women.
Macrolides (e.g., Erythromycin):
- Bind to the 50S subunit, blocking translocation during protein synthesis.
- Used as an alternative in penicillin-allergic patients and for atypical pathogens.

Inhibition of Nucleic Acid Synthesis

Quinolones and Fluoroquinolones (e.g., Ciprofloxacin):
- Inhibit DNA gyrase and topoisomerase IV, preventing DNA replication.
- Resistance through mutations in target enzymes or efflux pumps.
Rifamycins (e.g., Rifampin):
- Inhibit RNA synthesis by binding to bacterial RNA polymerase, commonly used for tuberculosis.
Metronidazole:
- Disrupts DNA by generating free radicals, effective particularly in anaerobic bacteria.

Inhibition of Metabolic Pathways

Sulfonamides (Sulfa drugs):
- Act as competitive inhibitors of dihydropteroate synthase, blocking folic acid synthesis essential for nucleic acid production.
- High therapeutic index in humans since they do not synthesize folic acid.

Antibiotic Resistance

Resistance mechanisms include:
- Enzyme production such as beta-lactamase, which destroys the beta-lactam ring.
- Target modification leading to altered PBPs that prevent binding.
- Efflux pumps that actively expel the drug from bacterial cells.
- Horizontal gene transfer via transformation, transduction, or conjugation.

Key Concepts for Test Review

Comparison of Gram-positive and Gram-negative bacteria, focusing on cell wall differences and susceptibility to antibiotics.
Understanding bacterial growth phases; antibiotics are most effective during the log phase.
Review the basic structure of bacterial cells, including ribosomes and peptidoglycan layers.

Antibiotic Targeting

Gram-positive bacteria show higher susceptibility to antibiotics targeting the thick peptidoglycan layer.
Gram-negative bacteria may exhibit resistance due to their outer membrane, necessitating the use of specific antibiotics like aminoglycosides.

Antibiotic Classes

Beta-lactams target cell wall synthesis.
Fluoroquinolones inhibit DNA gyrase.
Macrolides and Aminoglycosides disrupt protein synthesis differently at ribosomal subunits.

Focus on Case Studies and Practical Examples

Vancomycin is crucial against MRSA and resistant Gram-positive infections.
Erythromycin serves as an alternative for those allergic to penicillin and is effective against atypical pathogens.

Common Exam Questions

Understand targeting mechanisms of fluoroquinolones and macrolides.
Identify how bacteria develop resistance to beta-lactams.
Compare Gram-positive and Gram-negative bacteria regarding cell wall structure and antibiotic susceptibility.

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Description

This quiz explores the mechanisms through which antibiotics function to combat bacterial infections. It covers vital processes such as the inhibition of cell wall synthesis, highlighting key classes like beta-lactams and their specific modes of action. Test your understanding of how these drugs effectively target and disrupt bacterial cells.