range:20-200 spread plates,30-300 pour plates
If you have too many colonies (over 300 on all) - make estimate with highest dilution factor
-you have not diluted the sample enough. >300x10^7 = >300x10^9 cfu/mL EST
Preparing Dilution Schedules:
Culture containing 2.4 x10^9 - we want to conﬁrm
Pour plates should look like this:
2.4 x 10^9 cells/ml
Need to dilute to 10^-9 to get original count
How do you know what dilution schedule to do?There are reference standards out there - speciﬁcations for
products - tolerances/ reference points for a baseline to go with and then taking into consideration the
handling- leaving it out overnight
Dilution schedule will be tested.
10^-2 dilutions - test tube volumes 9.9mL and your transfer volumes 0.1mL Pour plates- 1.0mL does not affect the results
Always take into account the amount plated.
Pour plates can be 1.0mL or 0.1mL
Spread plates always 0.1 mL because 1.0mL is too much. Be sure to distinguish between whether your plates come from a particular dilution or if you diluted to that measurement
by taking 0.1 mL for your plates.
Ensuring Food Safety
-adulterated: not only bacteria, non-permitted flavour enhancers, pesticides, hair, glass particles
Indicator organisms suggest something more serious