Microbial count on settle plate

How we can count less than 1 in grade A area.

@manojsingh Most of the people are confused with <1 cfu in grade A area. I’ll explain less than 1 count by the following example.
Suppose you exposed 5 plates in any room and you got the following count.
Plate ----------- Count (CFU)
Plate 1 ---------- 0
Plate 2 ---------- 1
Plate 3 ---------- 0
Plate 4 ---------- 2
Plate 5 ---------- 1

Now count in room is calculated by taking mean of all plates
Mean = (0+1+0+2+1)/5 = 0.8 cfu
It is called <1 cfu
I think it is clear now.

Is this rule is also applicable for B C and D grade area.

Suppose 5 plates are exposed in c grade room then mean will be considered for cfu count?

Yes, It applies everywhere.

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Mr ankur g
Can u explain about leak test of an autoclave,
How can decided leak test limit is 0.13 bar

Plate 2, 4 and 5 , this location out of specification its OOS ?

Take the mean of all 5 plate it should be <1cfu.

If we found mean value 5.2 then it will pass for grade b area.it will be considered as 5 or more than 5?

Rounding of number will be considered or not?

Yes, you can round off the values but it should not affect the results ie. pass to fail or fail to pass.
If you round off the 0.95 cfu then it will be 1.0 and your area having limit <1 will be failed in the count. Therefore, be careful during rounding off the values.

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In this case we have to consider 0.95 or 1

Of course 0.95 because rounding off will change the results pass to fail.

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