ISO 6887 (all parts) (2017) medium: Quarter-strength Ringer’s

Media control Food chain

Microorganisms and performance criteria for multipurpose media 'Quarter-strength Ringer's' used in Food chain microbiology according to ISO 11133.

  • Quantitative control of Dilution

  • Best Practice Quarter-strength Ringer's

    1. Use a reference material or test suspension with a known number of Escherichia coli and Staphylococcus aureus.
    2. 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;
    3. Immediately remove 0,1 mL of inoculated diluent and spread over the surface of a non-selective agar (reference medium) such as TSA (t0).
    4. Hold the inoculated diluent at ambient temperature for 45 min.
    5. Mix and then remove the same volume (0,1 mL) and plate again on the reference medium (t1).
    6. Incubate at (45 min 1h) for (20 °C to 25 °C).
    7. Count the colonies on the plates t0 and t1. The number of microorganisms at t1, shall be within ± 30 % of the initial count (t0).

    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 'Quarter-strength Ringer's' is based on the data displayed in this table according ISO 11133.