Microbial Techniques Flashcards
How do you culture microorganisms
1) transfer bacteria into an agar plate using an inoculating loop
2) close and seal then incubate
4 phases of a bacterial growth curve
Lag phase
Log phase
Stationary phase
Death phase
Explain what happens during the lag phase
1). Bacteria is newly introduced to an environment
2) slowly adapting to neutering medium
3) interphase occurs and the rna is replicated
Explain what happens during the log phase
It’s when the bacteria start to grow and reproduce exponential growth
Binary fission occurs the growth rate doubles each time and exceeds the death rate
There is no limiting facts
Explain what happens during the stationary phase
When the growth rate is equal to the death rate so therefore the population growth just stays stationary it staibilises at its maximum
What happens during the death phase
This is when the death phase increases as a greater rate the. The growth phase there is an increase in toxic from death bacteria as well as lack of the nutrient medium as a result
How would you conduct. Cell count
Dilute broth sample with equal volume of trypan
Use a calibrated haemocytimeter with a volume of 0.1 count the cells in each of the sets of squares and calculate mean.
3) number of bacterial cells = number of counted x 10^4 per cm^3
Explain the process of using a haemocytometer
1) the number given to a counting chamber designed to count the number of cells
Each has a central platform and a bride attached to count the cellls
What are the positives and negatives of using a haemocyometer
Pros
It gives an accurate and exact number of cells and it tell you exactly how many viable cells there are
Cons
It’s a very slow process and sometimes it can be expensive
Explain how turbidity works
Place a sample into. A curvette
Place into a colurimeter and pass light through ,ensuring either the transition or the absorbance
The greater the amount of bacteria there is a greater absorbance and a lower transmission
The positives and negatives about turbidity
Pros
It’s a very fast and easy process and gives a number of total cells
Cons
It doesn’t give an exact value of cell count
Explain how a spread plate works
Spread the sample of bad tears evenly over a spread dish and d count the number of cells that grow
What are the positives and negatives of spread plate
Pros
They give an exact number of cells and count the amount of living cells
cons
Very slow and expensive as you have to wait for bacteria to grow and culture to be able to see accurate results
Explain what the process of dry mass
1) weight the sample
Find the mass of sterile filter membrane
Filter the bacteria from broth culture
Heat the bacteria and filter membrane to 100
Until mass remains constant
Record the mass
What are the pros and cons of dry mass
Pros
Counts the number of living and dead cells
And is very fast
Cons
It’s not as accurate compared to other dilution and optical methods
What is a bactericidal antibiotic example penecilin
Bactericidal kills the bacteria and prevent the cell wall building
Penecilin in most effective against gram positive bacteria that heavily rely on cell wall
Penecilin inhibits the enzyme transpeptise which cross links chains in the cell without this the cell wall breaks
And can no longer withstand the turner pressure and causes cell to burst
What is bacteriostatic and an example tetracycline
Bacteriostativ prevents the growth repair and reproduction of bacteria but it doesn’t kill it lets the immune system kill the badcteirs on its own
Example tetracycline
Binds to the 70s ribosomes and prevents protein synthesis
Thus prevents proteins being produced and therefore cell replication and growth this is medical.y very useful
Tetracycline is very effective in inhibiting broad spectrum bacteria
