Antimicrobials Overview

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Questions and Answers

Which aminoglycoside is preferred for infections caused by Pseudomonas aeruginosa?

Tobramycin (correct)

Plazomicin

Sisomicin

Amikacin

What primarily limits the effectiveness of aminoglycosides against certain bacteria?

Poor oral absorption

Ineffective against gram-positive bacteria

Requires oxygen uptake (correct)

High toxicity levels

How do aminoglycosides primarily inhibit bacterial protein synthesis?

By binding to the 50S ribosomal subunit

By enhancing tRNA attachment

By binding to the 30S ribosomal subunit (correct)

By denaturing mRNA

What effect do aminoglycosides have on polysomes?

Cause breakup into nonfunctional monosomes Signup and view all the answers

What is a noted characteristic of aminoglycosides that affects their administration route?

Poor oral absorption Signup and view all the answers

What is the mechanism by which aminoglycosides cause misreading of mRNA?

Altering ribosome shape Signup and view all the answers

Which statement about the structure of ribosomal RNA is true?

16SrRNA is associated with the 30S subunit Signup and view all the answers

What is a significant toxic effect of aminoglycosides related to their mechanism of action?

Formation of incorrect protein folds Signup and view all the answers

What role does IF-1 play during the initiation of protein synthesis?

Blocks the A site Signup and view all the answers

What occurs immediately after the association of the 50S subunit with the 30S initiation complex?

IF-3 is released Signup and view all the answers

What is the primary mode of action of tetracyclines?

Reversible binding to the 30S ribosome subunit Signup and view all the answers

Which initiator factor hydrolyzes GTP to provide energy for ribosomal assembly?

IF-2 Signup and view all the answers

Which mechanism is NOT associated with bacterial resistance to tetracyclines?

Inhibition of cell wall synthesis Signup and view all the answers

Which of the following is NOT a characteristic feature of aminoglycosides?

Contains a single six-membered ring Signup and view all the answers

What is a primary use of Streptomycin?

Combination therapy for tuberculosis Signup and view all the answers

What type of toxicity is specifically associated with tetracycline use during pregnancy?

Hepatotoxicity Signup and view all the answers

Which amino group-containing structure is part of the aminoglycoside classification?

Amino sugar with a six-membered ring Signup and view all the answers

What can reduce the absorption of tetracycline when taken together?

Antacids containing calcium or magnesium Signup and view all the answers

Which of the following is a potential side effect of tetracycline that affects the appearance of teeth?

Enamel discoloration and hypoplasia Signup and view all the answers

Which aminoglycoside is primarily used for serious Gram-negative infections?

Gentamicin Signup and view all the answers

Which condition might result from the deposition of tetracyclines in the growing bones?

Stunted growth Signup and view all the answers

Which step is NOT part of the transition to the 70S initiation complex?

GTP hydrolysis by IF-1 Signup and view all the answers

Which class of drugs has been developed to overcome some tetracycline resistance mechanisms?

Glycylcyclines Signup and view all the answers

What is a characteristic of ribosome protective proteins (RPPs) related to tetracycline resistance?

They shield the ribosome from tetracycline binding Signup and view all the answers

What is the primary mechanism of action of fluoroquinolones?

Inhibition of DNA gyrase and topoisomerases Signup and view all the answers

Which of the following statements about fluoroquinolones is correct?

They have a broad spectrum of activity against both gram-positive and gram-negative organisms. Signup and view all the answers

What can reduce the absorption of fluoroquinolones when taken orally?

Antacids Signup and view all the answers

What is the main action of quinupristin on the ribosomal subunit?

It prevents elongation of the polypeptide chain. Signup and view all the answers

Which enzyme is primarily targeted by fluoroquinolones in gram-negative bacteria?

DNA gyrase Signup and view all the answers

Which of the following organisms is quinupristin NOT effective against?

Enterococcus faecium Signup and view all the answers

What is a notable feature of quinupristin's action against Staphylococcus aureus?

Prolonged post-antibiotic effect lasting up to 10 hours. Signup and view all the answers

What is the parent compound of the fluoroquinolone class?

Nalidixic acid Signup and view all the answers

What mechanism of resistance against streptogramins B is caused by the vgb gene?

Hydrolysis of the antibiotic. Signup and view all the answers

What role does DNA gyrase play in bacterial DNA replication?

Relaxes tightly wound chromosomal DNA. Signup and view all the answers

Which resistance mechanism results from the action of erm genes?

Methylation of rRNA. Signup and view all the answers

Which fluoroquinolone is known for treating a broader range of infections, including anaerobic organisms?

Levofloxacin Signup and view all the answers

Which of the following is NOT a mechanism of resistance described for MLS antibiotics?

Mutation of the gene encoding the antibiotic. Signup and view all the answers

Why are fluoroquinolones increasingly used in clinical practice?

They exhibit relatively high safety and favorable pharmacokinetics. Signup and view all the answers

Which phenotype is most commonly associated with ermA and ermC genes?

Constitutive or inducible MLSB resistance. Signup and view all the answers

Which of the following best defines the term 'MLSB resistance'?

Resistance to macrolides, lincosamides, and streptogramin B. Signup and view all the answers

What is a key characteristic of Fidaxomicin's absorption when administered orally?

It is minimally absorbed into the bloodstream. Signup and view all the answers

Which bacteria does Fidaxomicin predominantly target?

Clostridium difficile Signup and view all the answers

What is the mechanism of action of Fidaxomicin?

Inhibition of DNA-dependent RNA polymerase. Signup and view all the answers

Which of the following statements is true about the use of Fidaxomicin in conjunction with Vancomycin?

It increases the curing rate and decreases the rate of recurrence. Signup and view all the answers

What is a notable limitation of Fidaxomicin?

It is costly and not first-line due to price. Signup and view all the answers

Which type of infection is primarily treated with Fidaxomicin?

Gastrointestinal infections caused by Clostridium difficile. Signup and view all the answers

Fidaxomicin is classified as which type of antibiotic?

Narrow-spectrum macrocyclic antibiotic. Signup and view all the answers

What type of resistance mechanism is associated with Fidaxomicin?

Mutation of DNA-dependent RNA polymerase. Signup and view all the answers

Study Notes

Antimicrobials

Antimicrobials are broadly divided into five categories: antibiotics, antivirals, antifungals, antiparasitics, and non-antibiotic antimicrobials.

Antibiotics

Antibiotics are substances produced by microorganisms that selectively suppress the growth of or kill other microorganisms at deficient concentrations.
They are chemotherapeutic agents with selective toxicity against bacteria, protozoa, fungi, and helminths.
Antimicrobials include chemotherapeutic agents and antibiotics.
Antibacterial agents interfere with bacterial growth and reproduction.
Bactericidal antibiotics kill bacteria.
Bacteriostatic agents inhibit bacterial growth.

Classification of Antimicrobials

Classified by chemical structure, mechanism of action, type of organisms (against which primarily active), spectrum of activity, type of action (bacteriostatic and bactericidal), and source of antibiotics.
Narrow-spectrum antimicrobials affect a limited number of microbial species.
Broad-spectrum antimicrobials affect a wide range of microbial species.

Antibiotic Resistance

Antimicrobial resistance (AMR) occurs when bacteria, viruses, fungi, and parasites no longer respond to antimicrobial medicines.
This is due to genetic changes in pathogens accelerated by human activity, mostly the misuse and overuse of antimicrobials.

Mechanisms of Resistance

Permeability alteration changes the cell wall permeability/nature of the outer membrane.
Enzymes production breaks down the antimicrobial.
Altered structure target changes/alters the target/receptor.
Altered metabolic pathways bypass the reaction inhibited by the drug.

Antimicrobial Resistance (AMR)

Antimicrobials no longer work on pathogens
Resistance leads to difficult or impossible infection treatment
Rise in resistance risk of disease spread, severe illness, disability and death
Natural process of pathogens changing over time through genetic changes
Speed of this process accelerated by human activity (overuse of antimicrobials to treat, prevent or control infections)

Mechanisms of Action of Antibiotics

Inhibit cell wall synthesis
Disrupt cytoplasmic membrane
Inhibit bacterial protein synthesis
Inhibit nucleic acid synthesis
Inhibit folic acid synthesis

Overview of Protein Synthesis

Replication
Transcription
Translation
Ribosome
Amino acid activation
Initiation complex formation
Peptide bond formation and elongation
Translocation and termination
Release and recycling ribosome

1. Mupirocin

Naturally synthesized antibiotic agent isolated from Pseudomonas fluorescens
Used as a topical treatment for bacterial skin infections (impetigo, furuncles, and open wounds).
Effective against methicillin-resistant Staphylococcus aureus(MRSA)
Bactericidal at high concentrations, bacteriostatic at low.

2. Aminoglycosides

Naturally occurring substances produced by actinomycetes
Exhibit both bactericidal and bacteriostatic effects.
Act on the 30S ribosomal subunit, causing misreading of mRNA.
Typically used for serious Gram-negative infections.
Resistance can arise from mutations in target sites and/or production of enzymes that inactivate the drug.

3. Oxazolidinones (Linezolid)

Inhibits bacterial protein synthesis by binding to 23S rRNA of the 50S ribosomal subunit
Effective against Gram-positive bacteria.
Effective against bacteria resistant to other agents (like methicillin-resistant S. aureus)
Resistance can arise from mutations in the 23S rRNA target site and the presence of efflux pumps.

4. Tetracyclines

Bacteriostatic antibiotics that inhibit protein synthesis by blocking the attachment of tRNA to the 30S ribosomal subunit.
Effective against several bacterial types(aerobic and anaerobic).
Resistance mechanisms include mutations in ribosomal targets and active efflux.
Resistance may arise from alterations in transport into bacterial cells.

5. Macrolides

Bacteriostatic agents that interfere with protein synthesis by binding to the 50S subunit.
Effective mainly against Gram-positive bacteria and some atypical bacteria.
Multiple resistance mechanisms can exist. (Reduced permeability/efflux of the drug)

6. Lincosamides

Bacteriostatic agents that inhibit protein synthesis by binding to the 50S subunit of the bacterial ribosome leading to inhibition of peptide bond formation during bacterial protein synthesis
Clinically relevant for treating infections caused by both Gram-positive and Gram-negative organisms.
Resistance: primarily plasmid-mediated.

7. Pleuromutilins

Naturally synthesized antibiotics from a fungus, inhibit bacterial protein synthesis by binding to peptidyl transferase center of the 50S ribosomal subunit of the ribosome
Effective in treating a broad range of Gram-positive bacteria.
Resistance: reduced susceptibility to the drug through mutations in the target site or efflux pumps.
Most effective against Gram-positive bacteria, also effective against bacteria causing skin or ocular infections.

8. Chloramphenicol

Broad-spectrum antibiotic that inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit, preventing peptide bond formation.
Primarily bacteriostatic but with some bactericidal activity against some organisms.
Resistance mechanisms: primarily involve the production of chloramphenicol acetyltransferase (CAT) enzymes.

9. Streptogramins

Bactericidal antibiotics that inhibit protein synthesis. They act on both the 50S and 30S ribosome subunits leading to decreased bacterial protein synthesis
Primarily effective against Gram-positive bacteria
Resistance develops by ribosome mutations, and/or bacterial efflux mechanisms.

10. Fusidic acid

Bacteriostatic antibiotic targeting elongation steps in bacterial protein synthesis by binding to EF-G, causing blockage of this step and stopping elongation.
Resistance can arise if EF-G is altered so it no longer binds to fusidic acid or from active efflux pumps.

11. Fidaxomicin

First-line treatments for Clostridium difficile infections; Bactericidal.
Acts by inhibiting DNA-dependent RNA polymerase (an enzyme essential for bacterial RNA synthesis and transcription).

12. Rifamycins

Interfere with bacterial RNA synthesis; Bactericidal.
Treatment of tuberculosis, and other infections
Resistance arising from mutations in the RNA polymerase (rpoB) gene.

13. 5-Nitroimidazoles

They damage bacterial DNA through the formation of highly reactive radicals
Broad range activity; used for treatment of specific anaerobic bacteria and pathogens
Resistance arises due to mutations in the target enzyme and/or the alteration of cellular uptake of the drug.

14. 5-Nitrofurans

Inhibit bacterial protein synthesis (bactericidal). Effective treatment for urinary tract infections
Resistance observed due to variations in the bacterial target sites
Resistance may arise from mutations or different types of efflux pumps.

15. Fluoroquinolones

Inhibit bacterial DNA replication by blocking DNA gyrase, a bacterial enzyme crucial for DNA supercoiling
Effective against many bacteria and other pathogens (Gram-negative).
Resistance is possible due to mutations within the targets of the drug, or bacterial resistance associated with efflux pumps.

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Description

This quiz covers the classification and types of antimicrobials, including antibiotics, antivirals, antifungals, and antiparasitics. Test your knowledge on the mechanisms of action, spectrum of activity, and the differences between bactericidal and bacteriostatic agents.