Microorganisms Flashcards
(36 cards)
In what ways can you grow/culture bacteria?
- Nutrient broth solution
- Colonies on an agar plate
How often can bacteria replicate?
Approximately every 20 mins
How do bacteria replicate?
Binary fission
How can microorganisms grow in a nutrient broth?
The liquid/gel provides al the nutrients the bacteria needs to grow successfully, including:
- Carbohydrates for energy
- Nitrogen for protein synthesis
- Minerals
How are agar plates created?
By pouring hot molten agar into sterile petri dishes and allowing it to set
What are aseptic techniques?
Procedures to prevent contamination from pathogens
What are aseptic techniques?
Procedures to prevent contamination from pathogens
Why is it important to use aseptic techniques on all apparatus when culturing microorganisms?
To prevent contamination from skin, air, soil, and water. This kills and prevents entry of unwanted bacteria
What aseptic techniques are used in the culturing of microorganisms?
Flames
Temperature
Boiling
Lids
How is management of lids used as an aseptic technique?
To prevent air from getting into the Petri dish, the lid must be quickly removed and replaced when transferring bacteria to the agar using the inoculating loop. Lid should be taped on and the dish should be stored upside down to prevent condensation forming on the lid and then dripping onto the agar.
How is boiling used as an aseptic technique?
Solutions and agar must be boiled for sterilisation
How is management of temperature used as an aseptic technique?
In schools the maximum temperature at which cultures should be incubated is 25’C which reduces the risk of harmful bacteria growing.
How are flames used as an aseptic technique
Inoculation loops must be passed through a flame for sterilisation
What can cultures of bacteria be used for?
To investigate effects of antibiotics and disinfectants
What is the inoculating loop used for?
To transfer bacteria onto the agar plate
How would you know if a sample has been contaminated?
If there are colonies of different colours observed on the Petri dish
Why shouldn’t we seal the Petri dish all the way around before storing?
We want oxygen to get in so harmful anaerobic bacteria doesn’t grow
What effect does temperature have on the growth and development of bacteria?
Cell metabolism (chemical reactions) in bacteria is controlled by enzymes. Increasing temp. up to 37 degrees speeds up rate of reactions as this is the optimum temperature for the enzymes to function Higher than 37 degrees and the enzymes denature (e.g. cooking food kills bacteria) Low temperatures do not kill bacteria but considerably slow down/stops reproduction of bacteria depending on how cold it is (e.g. fridges slow it down at 4 degrees, freezers stop it at -20 but does not kill them)
What equation would be used to calculate the areas of bacteria killed by an antiseptic/antibiotic, and what would this indicate?
A = πr2
Area = π x radius2
The largest area cleared indicates the most effective antibiotic/antiseptic.
How can a future population of bacteria be estimated?
By multiplying the current population by two for every mean division time (time it takes for the bacteria to divide) that passes
- Calculate how many times the bacteria divide in 6h
e. g. if a bacteria divides every 20m it will divide 3x each hour. If it grows for 6h, this will be 3x6=18 times - Calculate number of bacteria in population
Use equation:
Number of bacteria at beginning of growth period x 2^number of divisions
How can we test the effectiveness of an antibiotic?
By applying antibiotic-containing paper disks to agar plates incubated with a species of bacteria.
If the antibiotic stops the bacteria from growing or kills the bacteria there will be an area around the disk where the bacteria have not grown enough to be visible called a ZONE OF INHIBITION
What is a zone of inhibition?
The area around a sample of an antibiotic where bacteria hasn’t been able to grow
How would you perform an experiment investigating the effect of antibiotics on bacterial growth?
- Flame forceps and use them to pick up a paper disk and dip it into antibiotic A
- Allow them to dry for 5 minutes on an open, sterile Petri dish, next to a lit Bunsen burner
- Repeat steps for antibiotics B, C, and D
- Turn an agar plate already prepared and seeded with bacteria upside down and divide the base into quarters laelled A, B, C, and D
- Flame forceps again and pick up antibiotic disk A. Raise the lid of the Petri dish and place the disk on the agar in the centre of section A
- Repeat step for other disks
- Tape lid securely and incubate upside down for 2-3 days at 20-25C
- Record width of each clear zone around the antimicrobials
What factors affect the rate at which populations of bacteria grow?
Moisture availability - Bacterial growth is usually fastest in moist conditions (which is why food is sealed in dry conditions)
Temperature - Growth rates are fastest in warm temperatures
