Thermophilic count

THERMOPHILIC COUNT

This method is used for determining the total number of thermophilic bacteria in milk. The method consists of mixing appropriate quantity of milk with suitable nutrient agar medium in a petridish and counting the bacterial colonies developed after incubation at a specified temperature for a definite period of time. This method is time consuming and expensive.

Apparatus required

  • 1.1 ml of pipettes, Petridishes, Petridish can, Pipette can, Conical flask, Incubator, Refrigerator, Autoclave, Hot air oven, Test tubes, Distilled water, SPC agar.

Procedure

  • Each plate is identified with sample number, dilution rate, date and time of plating.
  • Mix the milk sample by rotating between the palms before serially diluting the sample.
  • Plating should be done in a presterilized area and serial dilution of sample is done.
  • Transfer of serially diluted sample and the media into the petridish and should be done near the flame.
  • 1 ml of mixed milk sample is taken and is transferred to the 1st test tube containing 9 ml of sterilized distilled water (dilution blank).
  • The milk sample is mixed with the dilution blank by rotating between the palms before further serial dilution.
  • 1 ml of serially diluted sample is drawn from the 6th test tube and transferred to the petridish.
  • 10-15 ml of sterilized standard plate count agar at a temperature of 40-450C is transferred to the petridish.
  • The serially diluted milk sample in the petridish is mixed with the medium by rotating gently five times clockwise, 5 times anti clock wise, 5 times up and down and five times side ways.
  • Petridish is kept undisturbed for few minutes until the media gets solidified.
  • Then the petridish is inverted and kept inside the incubator maintained at 550C and incubated for 48 hours. All the colonies are counted. The number of colonies multiplied by the dilution factor gives thermophiles per ml of milk.

Calculation

Total Number of thermophiles = No. of organisms X Dilution factor = cfu per ml of milk.

Result

Comment

Questions

  1. Enumerate the significance of thermophiles in milk?
  2. Name the bacteria that is a misnomer for thermophile?
Last modified: Tuesday, 17 April 2012, 11:03 AM