Viable Counts: Dilution Arithmetic Quiz

1. Results of plating and enumerating bacteria are expressed as:
PKU
PFU
DUI
CFU
none of the above

2. The "countable range" used when enumerating bacterial colonies is:
15-150
400-750
340-440
30-300
All of the above may be used as statistically acceptable.

3. When calculating the final plate dilution:
We take the diameter of the plate to calculate the area occupied by bacteria
We divide by 0.157
We incorporate the size of the inoculum with the dilution factor.
We divide all the results by negative log of pH
None of the above are correct.

4. The total amount of material present is the amount of sample plus the amount of uncontaminated material used as the diluent. This is expressed mathematically as:
d = x / (x + y)
d = a+b
d = x+y
all of the above
none of the above

5. The following statements are false EXCEPT:
The final dilution in a serial dilution is the sum total of all the dilutions
The final dilution in a serial dilution is the product of all the dilutions that led up to it.
The final dilution in a serial dilution is the original number multiplied by 100
The final dilution is always the first tube dilution times 10
The final dilution is expressed mathematically as a+b

6. To obtain the concentration in the original sample, divide the measured result by the dilution from which the result was obtained.
True
False

7. To obtain the total amount of substance in a sample, multiply concentration by the amount of sample.
True
False

   

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