Culturing Bacteria Flashcards
(29 cards)
What is the purpose of using aseptic techniques when culturing bacteria?
To prevent contamination of the bacterial culture with unwanted microorganisms and to protect the experimenter from harmful microbes.
Why are Petri dishes and culture media sterilised before use?
To destroy any existing microorganisms and prevent contamination of the culture.
What is the ideal temperature for incubating bacteria in schools, and why?
25°C — it allows for bacterial growth but reduces the risk of growing pathogenic bacteria harmful to humans.
Why is the lid of the Petri dish taped on but not completely sealed?
To prevent airborne contamination while still allowing oxygen to enter, avoiding the growth of anaerobic bacteria.
What is the function of nutrient agar in culturing bacteria?
Iy provides a solid surface and essential nutrients for bacterial growth.
How are bacteria transferred to the agar plate during inoculation?
Using a sterile inoculating loop, often sterilised by passing through a flame before and after use.
What is the significance of using an autoclave in bacterial culturing?
It sterilises equipment and media using high-pressure steam at 121°C to kill all microorganisms, including spores.
How do you measure bacterial growth on an agar plate?
By observing and measuring the diameter of colonies or zones of inhibition around antibiotic discs.
What is the role of antibiotics in bacterial culture experiments?
To test bacterial resistance or susceptibility by observing the zone of inhibition.
Why should cultures not be opened after incubation?
To prevent the release of potentially harmful microorganisms into the environment.
What is the main goal of aseptic technique in microbiology?
To prevent contamination of cultures and ensure the safety of the experimenter.
Why should hands be washed and surfaces disinfected before starting bacterial culturing?
To eliminate existing microbes that could contaminate the experiment.
List three examples of aseptic technique.
1) Sterilising equipment before use
2) Flaming the neck of bottles
3) Working near a lit Bunsen burner to create an updraft.
What is the importance of using personal protective equipment (PPE) such as gloves and lab coats?
To protect the experimenter from exposure to harmful bacteria and prevent contamination of the culture.
Why are inoculating loops sterilised by heating until red hot?
To kill any residual microorganisms before transferring bacterial samples.
Why should the neck of culture bottles be flamed when opened and closed?
To kill airborne microbes near the bottle opening and maintain aseptic conditions.
What does an autoclave do, and what are its typical operating conditions?
It sterilises media and equipment using pressurised steam at 121°C for 15 minutes.
Why should agar plates be stored upside down during incubation?
To prevent condensation from dripping onto the agar surface and spreading colonies.
What is a pure culture?
A bacterial culture that contains only one species of microorganism.
What is nutrient agar, and what is its role?
A gel-like substance that provides nutrients and a surface for bacterial growth.
How can you isolate pure bacterial colonies on an agar plate?
By using the streak plate method to dilute the bacteria across the surface.
What is the difference between liquid and solid culture media?
Liquid media allows for dispersed growth in broth; solid media (e.g., agar) enables visible colony formation.
What are key factors that affect bacterial growth?
Temperature, pH, oxygen availability, and nutrient availability.
Why must anaerobic conditions be avoided when culturing unknown bacteria?
Anaerobic conditions may favour harmful or pathogenic species.
