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Questions and Answers
What is the mechanism of action of Penicillins & Cephalosporins?
What is a characteristic of Plasmid-Mediated Resistance?
What is the function of R factors in Plasmid-Mediated Resistance?
What is the mechanism of resistance to Penicillins & Cephalosporins?
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What is Transposon-Mediated Resistance?
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What is the function of Clavulanic acid and Sulbactam?
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What is the mechanism of resistance that involves the production of enzymes that inactivate the drug?
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Which type of resistance is often mediated by mutations in the gene encoding a drug target?
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What is the term for the genetic basis of drug resistance mediated by genetic change in bacteria?
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Which of the following is an example of a type of antibiotic drug that can be inactivated by enzymes?
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What is the term for the type of resistance that cannot be overcome by increasing the dose of the antibiotic?
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How many types of genetic basis of drug resistance are there in bacteria?
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What is the mechanism of resistance to carbapenems in bacteria?
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How do bacteria resist the action of tetracyclines?
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What is the mechanism of action of quinolones in bacteria?
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How do bacteria resist the action of sulfonamides?
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What is the mechanism of resistance to chloramphenicol in bacteria?
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What is the mechanism of resistance to trimethoprim in bacteria?
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What is the mechanism of resistance to quinolones?
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Why are antibiotic combinations used in the treatment of infections?
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What is a consequence of the overuse and misuse of antibiotics?
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Why are antibiotics used in animal feed?
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What is the purpose of antibiotic sensitivity testing?
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What is the Disk Diffusion Method used for?
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What is a consequence of the emergence of resistant organisms?
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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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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.
