what is the principal of standard plate count technique?
Answers
Standard Plate Count (SPC)
This method consists of growing the bacteria in a nutrient culture petridish or (petrifilm) and counting colonies which develop. It can be used for all types of dairy products and is generally used in the examination of Grade A raw and pasteurized milk. This method used to determine the general quality of the milk supply.
Procedure
1. Wash the hands and disinfect the stage.
2. Mixing of milk sample.
3. Make a series dilutions of milk sample.
4. Transfer a suitable dilution to a petridish by sterile pipette.
5. Add a suitable amount (12 ml ) from SPC agar on the dilution and mixing
gently by moving the dish on different direction.
6. Incubate 48 hours at 32°C .
7. Count colonies and report results.
Note: Choosing the plates with ( 25 - 250 ) colonies
SPC(Cfu/ml)= Average number of colonies x Reciprocal of the dilution used
Counting: mean estimate of bacterial populations and it is not exact because:-
1. The agar used in method (SPC agar) is not suitable for growing all species of bacteria.
2. Incubation Degree which used in method (32°C) is not suitable for growing all species of bacteria.
3. Sharing more than one bacteria to form one colony.