6. Investigation Selection Flashcards
What are antimicrobial substances?
Substances that kill microorganisms eg antibiotics, antiseptics.
Investigating the effects of antimicrobial substances on microbes shows what?
Whether the microbes have evolved resistance to these substances or not.
What are antibiotics?
Medicines that kill antibiotics making them a type of antimicrobial substance.
The whole investigation must be carried out using what?
Aseptic techniques.
What is the bacteria you are going to be using have been grown in?
A liquid broth.
Mixture of distilled water, bacterial culture and nutrients.
What do you do with the innoculation loop?
It needs to be sterilised in Bunsen burner and then transfer the bacteria from the broth to an agar plate.
Spread bacteria over plate using loop.
What do you place onto the plate?
Sterile paper discs soaked in different antibiotics spaced apart.
Various concentrations of antibiotic.
As well as the sterile paper discs what else do you need to add?
A negative control disc soaked only in sterile water.
What do you do when the lid is taped onto the petri dish?
Invert and incubate at about 25 degrees for 48 hours.
Allows bacteria to grow forming a lawn
What is the inhibition zone?
Anywhere the bacteria can’t grow can be seen as a clear patch in the lawn of the bacteria.
What does the size of the inhibition zone tell you?
How well the antibiotic works.
LARGER THE ZONE = MORE BACTERIA WERE INHIBITED FROM GROWING.
What is a negative control supposed to do?
Not have any effect on the experiment.
Why don’t you completely seal the petri dish?
It will prevent oxygen from entering the dish, which may encourage the growth if anaerobic disease-causing bacteria.
Why are aseptic techniques used?
To prevent contamination of cultures by unwanted microorganisms.
Important because contamination can affect growth of microorganisms.
What must you disinfect?
Work surfaces before you start work to minimise contamination. Disinfect again after work.
