Microorganisms and performance criteria for testing non-selective media 'YEA' for Enumeration of Total flora used in Water quality microbiology according to ISO 11133.
Quantitative control of Productivity
- Use a quantitative reference material or test suspension with a known number of Escherichia coli.
- Dilute this material so 50 to 120 cfu is inoculated on the YEA by pouring for example 1 mL.
- Do this also for the reference media (Media batch YEA already validated).
- Incubate at (36 ± 2) °C for (44 ± 4) h.
- Count the colonies on the medium under test (YEA) and the reference media (Media batch YEA already validated).
- Calculate the productivity ratio PR. The criteria is: PR ≥ 0,7.
- If the PR exceeds 1,4 identify the reason.
- For this the total count of colonies obtained on the culture medium under test (YEA) is divided by the total count of colonies obtained on the defined reference medium (Media batch YEA already validated).
Best Practice YEA
Quantitative control of Productivity solid medium
|Calculate the productivity ratio PR as follows:||PR||NS|
|Ns = total count test medium|
|N0 = total count reference medium|
|Control strain||WDCM number||Ref. media||Incubation||Criteria||Characteristic reaction|
|Escherichia coli||Media batch YEA already validated||(36 ± 2) °C for (44 ± 4) h||PR ≥ 0,7||Growth|
|Bacillus subtilis subsp. spizizenii|
|The best practice for Quantitative control of Productivity for media control of 'YEA' is based on the data displayed in this table according ISO 11133.|