Development of Resistance to Chemotherapeutic Agents (Optional) Flashcards
Pharm. Chijioke
What does it mean for bacteria strains to be resistant to an antimicrobial agent?
Bacteria strains are resistant when the MIC or MBC of the agent is so high that the usual effective dose is no longer effective.
What was a significant observation in the early days of penicillin production?
Not all bacteria were killed by the antibiotic.
What are the two main theories on the origin of resistance?
- Pre-existing mutants of the resistant strain
- Resistance due to exposure of organisms to the antibiotics
What does the theory of pre-existing mutants suggest?
It suggests that the resistant mutant pre-exists any contact with the antimicrobial agent.
How can bacteria develop resistance through exposure?
Bacteria can develop resistance through contact with sub-lethal levels of the antimicrobial agent.
What is acquired resistance?
Resistance that occurs in vivo, in patients during the course of their treatment with particular chemotherapeutic agents.
What factors are related to the occurrence of acquired resistance?
The frequency and inadequacy of antibiotic use.
What can reverse acquired resistance in organisms?
A total withdrawal of an agent for a sufficiently long period.
What is induced resistance?
Resistance produced in laboratory strains of microorganisms through exposure to increasing sub-inhibitory concentrations of antimicrobial agents.
What is cross-resistance?
When a variant strain becomes resistant to other compounds concurrently due to its resistance to one agent.
In which class of antibiotics is cross-resistance almost uniformly true?
Tetracyclines.
What is multiple resistance?
When a microorganism develops resistance to different unrelated antimicrobial agents at different times.
Which bacteria are notably known for multiple resistance?
Resistant strains of Staphylococci.
What are the two bases of bacteria resistance?
- Biochemical basis of resistance
- Genetic basis of resistance
What can cause resistance in biochemical terms?
- Modification of the target enzyme
- Reduction of physiological importance of the target enzyme
- Permeability changes against antibiotics
- Synthesis of an enzyme that inactivates the inhibitor
What is the genetic basis of resistance important for?
It helps in determining the evolutionary origin of resistance.
What can gene mutation lead to?
Biosynthesis of a modified target organ.
What are chromosomal additional genes?
Genes attached to the original chromosome that confer resistance.
What are extra chromosomal additional genes?
Genes that are not attached to the original chromosome.
What are plasmids also known as?
Resistance (R) factors.
What is a key property of plasmids?
They are self-replicating.
What is conjugation in the context of gene transmission?
The joining of two cells by means of their pili for R factor transfer.
What occurs during transformation?
Water soluble fragments of DNA are transferred from a donor cell to a recipient cell.
What is transduction?
A process where a temperate bacteriophage introduces a small portion of chromosomal DNA into a recipient cell.
