Genetic Basis of Resistance in Microorganisms
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Questions and Answers

What is the mechanism of action of Penicillins & Cephalosporins?

  • Inhibition of cell wall synthesis (correct)
  • Inhibition of electron transport chain
  • Inhibition of DNA replication
  • Inhibition of protein synthesis

    • What is a characteristic of Plasmid-Mediated Resistance?

  • It can transfer from one cell to another by conjugation (correct)
  • It mediates resistance to a single drug
  • It only occurs in gram-positive bacteria
  • It is a permanent change in the bacterial chromosome

    • What is the function of R factors in Plasmid-Mediated Resistance?

  • To encode the target of the drug
  • To mediate drug resistance
  • To replicate independently of the bacterial chromosome (correct)
  • To encode the transport system in the membrane

    • What is the mechanism of resistance to Penicillins & Cephalosporins?

    <p>Inactivation by β-lactamases</p> Signup and view all the answers

    What is Transposon-Mediated Resistance?

    <p>The transfer of resistance genes within or between large pieces of DNA</p> Signup and view all the answers

    What is the function of Clavulanic acid and Sulbactam?

    <p>To bind strongly to β-lactamases and inactivate them</p> Signup and view all the answers

    What is the mechanism of resistance that involves the production of enzymes that inactivate the drug?

    <p>Enzymatic inhibition</p> Signup and view all the answers

    Which type of resistance is often mediated by mutations in the gene encoding a drug target?

    <p>Low-level resistance</p> Signup and view all the answers

    What is the term for the genetic basis of drug resistance mediated by genetic change in bacteria?

    <p>Molecular genetics of antibiotic resistance</p> Signup and view all the answers

    Which of the following is an example of a type of antibiotic drug that can be inactivated by enzymes?

    <p>All of the above</p> Signup and view all the answers

    What is the term for the type of resistance that cannot be overcome by increasing the dose of the antibiotic?

    <p>High-level resistance</p> Signup and view all the answers

    How many types of genetic basis of drug resistance are there in bacteria?

    <p>3</p> Signup and view all the answers

    What is the mechanism of resistance to carbapenems in bacteria?

    <p>Production of carbapenemases that degrade the β-lactam ring</p> Signup and view all the answers

    How do bacteria resist the action of tetracyclines?

    <p>By reducing the uptake of the drug through plasmid-encoded processes</p> Signup and view all the answers

    What is the mechanism of action of quinolones in bacteria?

    <p>Inhibiting DNA synthesis by blocking DNA gyrase</p> Signup and view all the answers

    How do bacteria resist the action of sulfonamides?

    <p>By chromosomal mutations in the gene coding for dihydropteroate synthetase</p> Signup and view all the answers

    What is the mechanism of resistance to chloramphenicol in bacteria?

    <p>By a plasmid-encoded acetyltransferase that acetylates the drug</p> Signup and view all the answers

    What is the mechanism of resistance to trimethoprim in bacteria?

    <p>By chromosomal mutations in the gene coding for dihydrofolate reductase</p> Signup and view all the answers

    What is the mechanism of resistance to quinolones?

    <p>Modifying the bacterial DNA gyrase</p> Signup and view all the answers

    Why are antibiotic combinations used in the treatment of infections?

    <p>To prevent the emergence of resistant organisms</p> Signup and view all the answers

    What is a consequence of the overuse and misuse of antibiotics?

    <p>Selection of resistant organisms</p> Signup and view all the answers

    Why are antibiotics used in animal feed?

    <p>To promote animal growth and prevent infections</p> Signup and view all the answers

    What is the purpose of antibiotic sensitivity testing?

    <p>To determine the antibiotic resistance of an organism</p> Signup and view all the answers

    What is the Disk Diffusion Method used for?

    <p>To perform antibiotic sensitivity testing</p> Signup and view all the answers

    What is a consequence of the emergence of resistant organisms?

    <p>Decreased treatment options</p> Signup and view all the answers

    Study Notes

    Genetic Basis of Resistance

    • Chromosome-mediated resistance: mutation in gene coding for target of the drug or transport system in membrane controlling drug entry into cells
    • Plasmid-mediated resistance: occurs in many species, especially gram-negative rods; plasmids mediate resistance to multiple drugs; high rate of transfer from one cell to another, usually by conjugation
    • R factors: resistance plasmids with two sets of genes; resistant transfer genes (encode sex pilus and proteins for plasmid DNA transfer during conjugation) and drug resistance genes (encode proteins for drug resistance)
    • R factors can replicate independently of bacterial chromosome; can be transferred to cells of the same or different species
    • Transposon-mediated resistance: transposon-resistance genes transferred within or between large pieces of chromosomal DNA or plasmids

    Mechanisms of Resistance

    • Enzymatic inhibition: bacteria produce enzymes that inactivate the drug (e.g., β-lactamases)
    • Alteration of target sites: altered ribosomal target sites, altered cell wall precursor targets, altered target enzymes
    • Alteration of bacterial membranes: outer membrane permeability, inner membrane permeability

    Penicillins and Cephalosporins

    • Mechanism of action: inhibition of cell wall synthesis
    • Mechanism of resistance: cleavage by β-lactamases (penicillinases and cephalosporinases); clavulanic acid and sulbactam are penicillin analogues that bind strongly to β-lactamases and inactivate them

    Level of Resistance

    • High-level resistance: resistance that cannot be overcome by increasing the dose of the antibiotic; often results from enzyme-mediated resistance (e.g., β-lactamases)
    • Low-level resistance: resistance that can be overcome by increasing the dose of the antibiotic; often results from mutations in the gene encoding a drug target

    Molecular Genetics of Antibiotic Resistance

    • Genetic basis of drug resistance: mediated by genetic change in bacteria; three types: chromosome-mediated, plasmid-mediated, and transposon-mediated resistance

    Other Antibiotics

    • Carbapenems: resistance caused by carbapenemases that degrade the β-lactam ring; produced by many enteric gram-negative rods (e.g., Klebsiella, Escherichia, Pseudomonas)
    • Tetracyclines: resistance due to failure of the drug to reach an inhibitory concentration inside the bacteria; caused by plasmid-encoded processes that reduce uptake or enhance transport out of the cell
    • Chloramphenicol: resistance due to plasmid-encoded acetyltransferase that acetylates the drug
    • Sulfonamides: resistance mediated by plasmid-encoded transport system that actively exports the drug out of the cell and chromosomal mutation in the gene coding for the target enzyme dihydropteroate synthetase
    • Trimethoprim and Quinolones: resistance due to mutations in the chromosomal gene encoding dihydrofolate reductase and chromosomal mutations that modify DNA gyrase, respectively

    Use of Antibiotic Combinations

    • To treat serious infections before the identity of the organism is known
    • To achieve an inhibitory effect against certain organisms
    • To prevent the emergence of resistant organisms

    Overuse and Misuse of Antibiotics

    • Overuse in humans: using multiple antibiotics when one would be sufficient, prescribing unnecessarily long courses of antibiotic therapy, using antibiotics in self-limited infections for which they are not needed, and overusing antibiotics for prophylaxis before and after surgery
    • Overuse in animals: using antibiotics in animal feed to prevent infections and promote growth; selects for resistant organisms in animals and may contribute to the pool of resistant organisms in humans

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    Antibiotic Resistance Lecture PDF

    Description

    This quiz covers the genetic basis of resistance in microorganisms, including chromosome-mediated resistance, plasmid-mediated resistance, and R factors. It explores how microorganisms develop resistance to multiple drugs through gene mutations and plasmid transfer.

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