Microorganisms and performance criteria for multipurpose media 'Quarter-strength Ringer's' used in Food chain microbiology according to ISO 11133.
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 Quarter-strength Ringer's
|Control strain||WDCM number||Ref. media||Incubation||Criteria||Characteristic reaction|
|Escherichia coli||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 'Quarter-strength Ringer's' is based on the data displayed in this table according ISO 11133.|