Antimicrobial Agents Overview

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Questions and Answers

Which mechanism is primarily associated with bactericidal antibiotics?

Inhibition of cell wall synthesis (correct)

Inhibition of nucleic acid synthesis

Inhibition of folic acid synthesis

Inhibition of protein synthesis

Which of the following antibiotics is known as a beta-lactam antibiotic?

Tetracycline

Penicillin (correct)

Chloramphenicol

Erythromycin

Which of the following antibiotics inhibits protein synthesis?

Sulfonamide

Polymyxin

Streptomycin (correct)

Neomycin (correct)

What is a common resistance mechanism that bacteria may develop against antibiotics?

Efflux pumps Signup and view all the answers

Which class of antibiotic is typically bacteriostatic?

Tetracyclines Signup and view all the answers

What is the primary action of sulfonamides on bacteria?

They inhibit the growth of bacteria. Signup and view all the answers

How do sulfonamides exert their effect against bacteria?

By acting as structural analogues of PABA. Signup and view all the answers

What is the consequence of excess PABA in the presence of sulfonamides?

It counters the inhibiting action of sulfonamides. Signup and view all the answers

Which enzyme is inhibited by trimethoprim to block folic acid formation?

Dihydrofolate reductase. Signup and view all the answers

What is the primary mechanism of action for penicillins?

They inhibit cell wall synthesis. Signup and view all the answers

Which of the following is a characteristic of bacterial resistance to sulfonamides?

Resistance is frequently caused by an R factor. Signup and view all the answers

Which form of bacteria is associated with lysis due to penicillins?

Protoplasts. Signup and view all the answers

What effect does adding side chains to penicillin have?

It prevents degradation of the B-lactam ring. Signup and view all the answers

What is the primary mode of action of cephalosporins?

Inhibition of cell wall synthesis Signup and view all the answers

Which of the following is a feature that distinguishes cephalosporins from penicillin?

Resistance to penicillinase Signup and view all the answers

What is the outcome of tetracycline binding to the 30S ribosomal subunit?

Inhibition of tRNA function Signup and view all the answers

What is a common resistance mechanism against aminoglycosides?

Mutation of ribosomal RNA Signup and view all the answers

What complication can arise from prolonged use of chloramphenicol?

Severe depression of bone marrow Signup and view all the answers

Which class of antibiotics primarily inhibits the function of DNA gyrase?

Quinolones Signup and view all the answers

Which antibiotic is known to cause liver damage as a complication?

Tetracycline Signup and view all the answers

What is the action of macrolides on the ribosome?

Bind to the 50S subunit Signup and view all the answers

Study Notes

Antimicrobial Agents

Antimicrobial agents are substances that kill or inhibit the growth of microorganisms.
Antibiotics are a type of antimicrobial substance produced by living microorganisms.
In 1877, Pasteur and Joubert observed that airborne contaminants had a lethal effect on Bacillus anthracis.
In 1929, Alexander Fleming observed that the fungus Penicillium notatum inhibited the growth of staphylococci.
Chain, Florey, and associates developed penicillin preparations with high antibacterial therapy but low toxicity for humans and animals.
A major source of antibiotics is Streptomyces.
Antibiotics are classified by their effect on bacteria.
- Bactericidal antibiotics kill bacteria.
  - Examples include penicillin, streptomycin, cephalosporin, polymyxin, neomycin, and erythromycin.
  - These have a rapid lethal effect in high concentrations.
- Bacteriostatic antibiotics inhibit bacterial growth.
  - Examples include tetracyclines, sulfonamides, and chloramphenicol.
  - Some can be both.

Mechanism of Action

Sulfonamides are bacteriostatic, inhibiting the growth of bacteria by acting as structural analogs of PABA.
- PABA is essential for the synthesis of folic acid, an essential metabolite for bacteria.
- Sulfonamides compete with PABA, hindering folic acid synthesis and consequently, inhibiting bacterial growth.
  - However, they do not affect bacteria that cannot synthesize their own folic acid.
Penicillins inhibit the synthesis of cell walls in growing susceptible bacteria.
- Bacteria's cell wall is composed of peptidoglycan.
- Penicillins prevent crosslinking of peptidoglycan, resulting in cell lysis.
  - Bacteria that lack cell walls are not affected.
  - Different procaine chains can influence the absorption.
Cephalosporins are synthetic analogs of penicillin.
- They have a lower toxicity and broader spectrum of activity than penicillins.
- They are effective against gram-positive and gram-negative bacteria.
Aminoglycosides inhibit protein synthesis.
- These bind to the 30S ribosomal subunit and interfere with the protein synthesis process within the cell.
  - This results in miscodding of proteins and peptide elongation.
- Potential mechanisms cause impaired ribosomal binding, transport, alteration/inactivation of the drug.
Tetracyclines inhibit protein synthesis.
- Bind to 30S ribosomal subunits and prevent the function of tRNA, which is crucial for protein production.
  - It is bacteriostatic and has a broad spectrum of effectiveness.
Chloramphenicol inhibits protein synthesis.
- Binds to 50S ribosomal subunits to suppress protein production.
  - Prolonged use may lead to bone marrow depression.
Macrolides (e.g., erythromycin) also inhibit protein synthesis. -Bind to 50S ribosome.
Lincosamides (e.g., clindamycin) also inhibit protein synthesis.
- Bind to a 50S ribosomal subunit.
Quinolones inhibit certain activities involving DNA.
- Inhibit the bacterial enzyme DNA gyrase, an activity crucial for supercoiling of chromosomal DNA.
  - This results in the degradation of DNA; resulting in bacterial death.

Mechanisms of Drug Resistance

Mechanisms for drug resistance include changes in outer membrane permeability, alterations in DNA gyrase, altered metabolic pathways, generation of antibiotic destroying enzymes, and alteration in the target.

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Description

This quiz provides an overview of antimicrobial agents, specifically focusing on antibiotics and their classifications. Explore the historical observations by Pasteur, Fleming, and others that led to the development of key antibacterial therapies. Test your knowledge on the mechanisms and examples of both bactericidal and bacteriostatic antibiotics.