Microorganisms and performance criteria for multipurpose media 'Diluents for special puposes' used in Food chain microbiology according to ISO 11133.
ISO 6887 (all parts) (2017) medium: Diluents for special puposes
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Quantitative control of Dilution
- Use a reference material or test suspension with a known number of Escherichia coli and Staphylococcus aureus.
- Inoculate a test portion (e.g. 9 mL) of the diluent with 1 mL of the test microorganism (Dilution liquids) suspension containing around 104 cfu/mL and mix;
- Immediately remove 0,1 mL of inoculated diluent and spread over the surface of a non-selective agar (reference medium) such as TSA (t0).
- Hold the inoculated diluent at ambient temperature for 45 min.
- Mix and then remove the same volume (0,1 mL) and plate again on the reference medium (t1).
- Incubate at (45 min 1h) for (20 °C to 25 °C).
- Count the colonies on the plates t0 and t1. The number of microorganisms at t1, shall be within ± 30 % of the initial count (t0).
Best Practice Diluents for special puposes
Control strain | WDCM number | Ref. media | Incubation | Criteria | Characteristic reaction |
---|---|---|---|---|---|
Escherichia coli | or | TSA | 45 min 1h for 20 °C to 25 °C | ±30 % colonies / T0 (±30 % of original count) | No characteristic colonies |
+ Staphylococcus aureus | |||||
The best practice for Quantitative control of Dilution for media control of 'Diluents for special puposes' is based on the data displayed in this table according ISO 11133. |