147 Enumeration of Bacteria (Spatula Method)

Methods Type: Generic Methods
Key data
Number: 147
Analyte: Bacteria (Spatula Method)
Matrix: Cereals, Cereal Products, Bread and Baked Goods, Pasta
Year of Approval: 1992
Scope: Cereals, Cereal Products, Bread and Baked Goods, Pasta
Principle: 
  • Since direct counting of the bacteria contained in or on the product under investigation is impossible, an indirect method has to be used.
  • The product under investigation is first mixed with a sterile physiological solution (6.1) in order to separate and suspend the microorganisms (8.1), where necessary, after grinding the product by means of blending equipment according to 5.2.1, 5.2.2 or 5.2.3.
  • A tenfold dilution series is made from this initial suspension (8.2).
  • Aliquots of the dilution stages are transferred onto the surface of a culture substrate that has previously been poured into sterile Petri dishes and has solidified (6.2.2).
  • The transferred suspension containing the microorganisms is uniformly spread over the surface of the culture substrate.
  • In the course of incubation the bacteria can multiply and form colonies on the surface of the culture substrate.
  • After the end of incubation the "number of bacteria per gram of sample" is calculated from the number of colonies present on the surface of selected plates of the culture substrate (9.1).

Definition

The bacteria count is the number of those colonies, that become visible due to the growth of mesophilic, either aerobic or facultatively anaerobic microorganisms after transfer of an aliquot of a suspension of the product under investigation to the surface of a suitable agar medium (6.2), spreading and subsequent incubation at 30 °C for 3 days (9.1).

 

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