Define Preparation of Dilutions - Standard or Total Plate Counts?

1. Serial dilution of homogenized sample in an appropriate diluent.

Preparation of dilutions - Decimal dilutions are prepared in a diluent [peptone water (1%) and 0.5% NaCl] and some dilutions are plated. Selection of the dilutions to be plated is made on the basis of expected microbial load in the sample.

2. Plating on to suitable agar medium by pour plate or surface plating.

3. Incubation of plates at appropriate temperature (usually 35-37°C) for a given time (24-48 hours).

4. Counting of all visible colonies manually or using a Quebec or electronic counter.

5. Calculating CFU/ml or CFU/gm of the food sample.