6.1 Microbial techniques Flashcards
What does ‘aseptic’ mean?
to prevent contamination
What are the aseptic techniques used in culturing microorganisms?
disinfecting surfaces
using a Bunsen burner (creating upward airflow)
heating neck of bottles and innoculating loops
What is a nutrient medium?
a substance used for the culture of microorganisms, which can be liquid (nutrient broth) or solid (nutrient agar)
What is nutrient agar?
jelly extracted from seaweed, used as a solid nutrient for culturing microorganisms, on a Petri dish
What is a nutrient broth?
a liquid nutrient for culturing microorganisms, commonly used in flasks, test tubes or bottles
What is a selective medium?
a growth medium for microorganisms containing a very specific mixture of nutrients, so only a particular type of microorganism will grow on it
Describe the cell counts method in measuring the growth of bacterial cultures.
bacteria in a nutrient broth can be counted using a microscope and haemocytometer.
- sample of nutrient broth is diluted with an equal volume of trypan blue dye.
- each corner of haemocytometer has 16 squares in each corner - so you can count number of cells in all 4 corners over time and calculate mean
Describe the dilution plating method in measuring the growth of bacterial cultures.
it is used to find the total viable cell count
colonies on an agar plate are grown from a single, viable, microorganism.
1cm3 of the original culture is diluted in 9cm3 of water - this is continued until the colonies can be counted
How would you calculate the total viable cell count?
number of colonies x dilution factor
Describe the optical methods in measuring the growth of bacterial cultures.
turbidity is used
the bacteria is cultured in a nutrient broth
as the bacteria grows, the solution becomes more cloudy/turbid
this can be placed into a colorimeter every 20 minutes to measure absorbance
the control/reference is plain nutrient broth
Describe the area and mass method in measuring the growth of bacterial cultures.
fungi can be cultures in a Petri dish to compare different growth rates in different conditions
you can check this by measuring the diameter of the fungi
the dry mass of fungi can be used to find optimum growth - heaviest
What are the 4 phases of a bacteria growth curve?
lag
log
stationary
death
What happens in the lag phase?
bacteria are adapting to their environment so they are not reproducing at maximum rate
What happens in the log phase?
when rate of bacterial reproduction is close to or at its maximum/optimum
What happens in the stationary phase?
total growth rate is 0
number of cells reproducing = number of cells dying
