12. Investigate the rate of growth of bacteria in liquid culture. Flashcards
1
Q
How can bacterial growth be measured?
A
Colorimetry.
This is a quick and relatively simple way of measuring growth. A disadvantage of measuring growth in this way is that is doesn’t provide a DIRECT count, and also counts non-viable bacteria.
To provide an indication of number of bacteria, colorimetry readings have to be related to bacterial count via a CALIBRATION CURVE produced using a HAEMOCYTOMETER.
2
Q
Method:
A
- Wash hands and disinfect bench area. Light a bunsen burner set to a safety flame in this same area.
- Collect a culture vessel containing sterile nutrient broth and inoculate using aseptic techniques. Using a measuring cylinder add 2 cm^3 of bacterial culture for every 10 cm^3 of broth. Swirl to mix. Place the culture vessel on the magnetic stirrer and stopper with cotton wool and aluminium foil.
- Place sterile culture medium into a cuvette and use this as a blank to set the absorbance of the colorimeter to zero. Keep this reference medium in the fridge between measurements. Perform this step quickly so that you can take the initial absorbance measurement as soon as possible.
- Measure 3 cm^3 into a clean cuvette and measure the absorbance. Record the date, time and absorbance in a table. Return the culture to the magnetic stirrer (incubate at no more than 30 degrees).
- Repeat steps 3 and 4 over the next 24 hours, taking several initial samples (20-30 minutes). If the optical density rises above a reading of 2 the results may become inaccurate and so sample dilution may be required. This can be accounted for when calculating the absorbance (multiply the reading by the dilution factor).
3
Q
What is inoculation?
A
The process by which a culture is introduced to a medium.
4
Q
What advantages does a light sensor have over a colorimeter?
A
The light sensor has advantages if it is used with a data logger because we can leave the yeast to culture while testing it continuously.
