Calculating CFU/g - Biology Forum

last updated by

SWEngineer 12 years, 11 months ago

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- November 25, 2011 at 10:29 am #15737
  SWEngineer
  Participant
  If we have a 5 gram food sample that was homogenised in sterile Ringer’s solution to give a total volume of 10 cm3. After that, if we serially dilute where 0.1 cm3 aliquots of a number of dilutions are spread plated on duplicate nutrient agar plates, and after incubation, we get for example the following colony counts in dilution 10-3:
  Dilution Replicate (1) Replicate (2)
  10-3 315 306
  I know how to calculate the CFU/cm3 of the homogenate. But, how do we calculate the average CFU/g of food sample?
  Thanks.
- November 25, 2011 at 11:36 am #108403
  JackBean
  Participant
  if 5 grams give 10 cm3, what is the factor to recalculate CFU/cm3 to CFU/g? 🙄
- November 26, 2011 at 11:27 am #108432
  SWEngineer
  Participant
  quote JackBean:
  if 5 grams give 10 cm3, what is the factor to recalculate CFU/cm3 to CFU/g? 🙄
  As I understood after asking, after calculating CFU/cm^3. We now say that this is for (5g/10cm^3), that is for 1/2 dilution, but here, we have to find it as a whole and not as a dilution.
  So, it will be: result of CFU/cm^3 * 1/0.5 = CFU/g of food sample
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