Microorganisms and performance criteria for reference media 'TSA' for Reference of Colony Count 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 and Clostridium perfringens and Pseudomannas aeroginosa.
- Dilute this material so 50 to 120 cfu is inoculated on the TSA.
- Use the same method of inoculation as described in the specific individual ISO 11133.
- Do this also for the reference media (Media batch TSA already validated).
- Count the colonies on the medium under test (TSA) and the reference media (Media batch TSA 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 (TSA) is divided by the total count of colonies obtained on the defined reference medium (Media batch TSA already validated).
Best Practice TSA
The best practice has been elaborated for Escherichia coli. The control strains mentioned in the table can be applied in the same way.
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 TSA already validated||for As specified in the method in which TSA is used as reference medium||PR ≥ 0,7||Characteristic colony according to each species|
|+ Clostridium perfringens|
|+ Pseudomannas aeroginosa|
|+ Enterococcus faecalis|
|The best practice for Quantitative control of Productivity for media control of 'TSA' is based on the data displayed in this table according ISO 11133.|