Unit 6- Microbial Techniques Flashcards
What are the different types of mixtures the microbes are cultured on?
- agar plate (made of agar and a nutrient broth)
- selective media
What is the agar plate?
A solid medium of agar mixed with a nutrient broth in a Petri dish
What is a a selective media?
A medium made of a specific recipe to allow the growth of only one group of microbes, it may include antiobiotics if the wanted bacteria is antibiotic resistant
How is equipment sterilised?
Using ultra violet
autoclave (large pressure cooker)
Using virkon, bleach or ethanol
Flaming
What conditions does a culture provide?
- nutrients
- suitable temp and pH
- usually access to O2
Aseptic techniques are used to avoid contamination, give some examples of aseptic techniques:
- all equipment should be sterile
- flame the appropriate equipment in Bunsen burner before and after
- replace lids as quickly as possible
What are the problems with culturing microbes?
- pathogens may enter the culture and grow risking disease
- safe organisms may mutate to dangerous strains
- contamination can spoil an investigation
What precautions can be taken to reduce the risk of culturing microbes?
- adequate O2 supply as pathogens prefer to grow in anaerobic conditions
- culture the medium at about 20 degrees for a few days as body temperature encourages the growth of potentially dangerous human pathogens
What 4 different techniques can be used to measure microbial growth?
- cell counting with haemocytometer
- turbidity with a colorimeter
- dilution plating until the microbes can be spread on an agar plate and counted
- weighing dry mass of a known volume
How can we measure the number of microbes in a culture broth by dilution plating?
- dilute the culture until the number of cultures can be counted when spread on an agar plate
(Dilution plating is the same as serial dilution)
How can you count the number of bacteria in a culture using a haemocytometer?
- Pipette the culture onto the haemocytometer
- the volume of the haemocytometer is 0.1mm
- count the number of cells in a 0.2mm box
- calculate the number of cells per mm^3
What is the convention when counting using a haemocytometer
Count the cells overlapping the north west boundary and discard the cells over the south east boundary
How do you only count living cells using a haemocytometer?
- add a vital stain (trypan blue) which only stains dead cells blue
What does turbidity mean?
Cloudiness
How can we measure cell density using a colorimeter?
- dilute the culture broth until it has an absorbable of below 0.5
- the greater the concentration of cells the more turbid the dilution giving a higher absorbance