Saddleback Journal of Biology - Saddleback College

Spring 2010 Biology 3B Paper
agar plate. This value was then multiplied by the
reciprocal of the volume of original undiluted
sample plated (dilution factor=175) to get the
colony forming units (CFU/mL). The following
equation was used to get the dilution factor for
bacterial growth under 300 colonies per plate:
equation was used to get the dilution factor for
bacterial growth over 300 colonies per plate:
The following equation was used to get the
colony forming units per milliliter for bacterial
growth under 300 colonies per plate:
Bacteria count for bacterial growth over
300 colonies per nutrient agar plate was
calculated by counting the colonies in a four
centimeter squared area to get representative
colony distribution. The sum of colonies in the
four centimeter squared area was divided by four
to get the average number of colonies per
centimeter squared. The average number of
colonies per centimeter squared was then
multiplied by 56.7 cm² (area of the nutrient agar
plate) to get the estimated number of colonies
per plate. The average number of colonies per
plate was then multiplied by the reciprocal of the
volume of original undiluted sample plated
(dilution factor = 17,500) to get the colony
forming units (CFU/mL). The following
.
*Note: One thousand is the dilution factor for
0.1 mL of diluted sample. This is the sample
volume that should be used when bacterial
counts are more than 300 colonies per plate.
The following equation was used to get the
colony forming units per milliliter for bacterial
growth over 300 colonies per plate:
Data were analyzed with Microsoft
Excel 2007, ANOVA, and post test software.
Results
Beef soup test tubes containing
deionized water control produced no bacteria and
remained sterile throughout the experiment.
Beef soup test tubes containing nutrient
broth control produced no bacteria and remained
sterile throughout the experiment
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Saddleback Journal of Biology
Spring 2010