Bio Practicals Flashcards
What does haemocytometry measure?
Total cell count
Preparation of a haemocytometry plate
- Well mixed cell culture sample is first diluted
- Then introduced to the central chamber via pipette
- Liquid flows under cover slip
- Sample viewed under microscope and no. of organisms in several squares is counted
- Average is calculated, multiplied by dilution factor gets you an estimate of the original number in the sample
Turbidimetry measures
Total cell count
Turbidimetry is measured using
Colorimeter
Turbidmetry preparation
- Culture sample is aseptically removed and thoroughly mixed before being placed in a cuvette.
- Cuvette is placed in the colorimeter and the optical density is measured as % absorbance.
- More cells present = greater turbidity
Cons of turbidmetry
Cannot distinguish living cells from dead cells
Cannot distinguish cells from particles of matter in the culture medium
To avoid inaccuracy created by particles of matter from the medium affecting the percentage absorbance, what precaution is taken?
Colorimeter is set to zero using a ‘blank’ cuvette which contains the culture medium alone
What does dilution plating measure
Viable counts
Methods of sterilisation
- Direct heat - inoculating loop, neck of tubes
- Autoclaving (120) - glassware, unwanted cultures
- Burning alcohol - quick sterilisation of glass
- Disinfectants - inanimate objects, e.g. Wood surfaces
Bioassay
Enables the effectiveness of a compound (antibiotic or disinfectant) to be determined by its effect on the growth of a microorganism
What can bioassays be used to screen and how
Microorganisms to determine if they produce an effective antibiotic.
Achieved by measuring their ability to inhibit the growth of bacteria on a bacterial lawn.
What does the diameter increase of a fungal mycelium measure?
Growth of filamentous fungi
Increase in dry mass measures
Growth rate of a variety of microorganisms
Problems with ORS containing more glucose
Lowered the water potential in the lumen of the small intestine cause diarrhoea to worsen
What polysaccharide is present in ORS and why
Starch as it is osmotically inactive and insoluble
It also is slowly broken down by amylase and maltose into glucose
This mean it can be taken up by co-transport at a normal rate