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Breed Counting Method


Breed Counting Method -

This method does not distinguish between live and dead cells. It is a direct count method in a known area of microscopic field.

The sample is spread (about 0.0 I ml) over I cm2 of a microscope slide. Milk smear is dried and stained with Newman - Lampert stain.

This stain fixes the smear, dissolves fat globules and stains bacteria with methylene blue. Slide is then scanned under several oil immersion microscopic fields. Calculation, are made as follows:


Area of one microscope field = 0.02 mm2.

Area over which milk sample is spread on the slide = 1 cm2 or 100 mm2

Then, no. of fields possible under the lens

= 100 mm2/(or divided by) 0.02 mm2

= 5000 fields

This number of field is for 0.01 ml of milk. However, final count is expressed as bacterial number per ml of sample. Thus, factor is to be multiplied by 100.

i.e. 5000 X 100 = 500,000


This is the microscope factor Le. 500,000

Suppose, 20 fields yielded an average of 0.4 bacteria per field. Then, the final count would be

0.4 X500, 000 (microscope factor)= 200,000 bacteria per ml of milk sample.
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