Practical 1. Microbial Offence and Defense Flashcards
What are bioassays used for ?
Used to estimate the concentration of antibiotics in a solution
Why do we need to be able to estimate the concentration of antibiotics in a solution ?
- During the manufacture of antibiotics
2. In a hospital setting, to measure the concentration of the antibiotic in a patients bloodstream
Where does a zone of growth of inhibition occur ?
Around the well
When does the edge of the zone of growth of inhibition form ?
When the antibiotic is too dilute to inhibit growth of the bacteria
What does a more concentrated antibiotic in the well result in ?
A wider zone of growth of inhibition
What can the standard curve be used for ?
To determine the antibiotic concentration in an unknown sample
What can antibiotics be synthesised by ?
- Fungi
2. Bacteria
What did the discovery of antibiotics for chemotherapy result in ?
The emergence of resistant organisms
How would you determine the sensitivity of an organism to antibiotics ?
A disc diffusion method
What must standardised methods for antibiotic disc diffusion consider the effects of ?
- Culture medium
- Inoculum density
- Antibiotic discs
- Incubation conditions
- Interpretation
What does susceptible mean ?
Implies that an infection caused by the strain may be treated with the antibiotic at the dosage recommended for the type of infection and the infecting species of bacterium, unless otherwise contra-indicated
What is meant by resistant ?
Encompasses strains incompletely inhibited within the usual therapeutic range
What is meant by the term intermediate ?
Strains exhibiting an in between diameter of zone of growth inhibition
How might resistance to antibiotics be acquired ?
- Chromosomal mutations
2. Transfer of plasmid determined resistance
What effect might a chromosomal mutation have on an antibiotic and give the example ?
Effect the functionality for example through alteration of the antibiotics target so that it is no longer susceptible
What is still retained in a chromosomal mutation ?
The functionality of the target molecule is retained
What is Rifampicin ?
An antibiotic
How does Rifampicin work ?
Binds to the enzyme RNA polymerase and blocks the ability of the bacterium to transcribe DNA into mRNA
How do mutations in chromosomal genes and Rifampicin work ?
Mutations in the chromosomal genes coding for RNA polymerase result in an altered enzyme to which rifampicin no longer binds, while maintaining functioning of the enzyme
Do chromosomal mutations occur frequently in bacteria populations ?
They occur spontaneously and at low frequencies
How can rifampicin resistant mutants be distinguished from rifampicin sensitive cells ?
By plating on agar containing rifampicin
Does plating on rifampicin containing media induce rifampicin resistant mutants ?
No, they are already present in the population
How can the frequency of rifampicin resistant mutants be calculated ?
Number of rifampicin resistant mutant colonies per ml/ starting culture viability count
What is another name for disc diffusion method ?
Kirby- Bauer Method
