Determining the total colony counts

In order to determine the colony count, 1 ml of water in each case is pipetted into a sterile Petri culture dish and mixed with sterile nutrient gelatine or sterile nutrient agar. Nutrient gelatine is liquefied in a water bath at 33 °C and cooled to about 30 C before pouring into the culture dish. Nutrient agar is liquefied in boiling water and cooled to 6 2 C 

Nutrient gelatine solidifies at temperatures below 23 C and cooling is therefore necessary in certain circumstances. 

If high counts are expected in the water to be examined, it is advisable to prepare series of dilutions with sterile water and then to test the dilution stages 1 100, 1 1000, etc. 

The culture with the solidified layer of nutrient medium is incubated at the prescribed temperature in the incubator or incubating chamber, whereby a maximum of to 6 plates should be stacked one above the other. Plates 

After the prescribed incubation period has elapsed, the visible colonies 

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