ISO 21527-2 (2008) medium: DG18

Media control Food and animal feeding stuffs

Microorganisms and performance criteria for testing selective media 'DG18' for Enumeration of Yeasts and moulds used in Food and animal feeding stuffs microbiology according to ISO 11133.

  • Quantitative control of Productivity

    • Best Practice DG18

    Quantitative control of Productivity solid medium

    1. Use a quantitative reference material or test suspension with a known number of Saccharomyces cerevisiae and Wallemia sebi.
    2. Dilute this material so 50 to 120 cfu is inoculated on the DG18 by spreading for example 0.1 mL.
    3. This can be a multi or single strain material.
    4. Do this also for the reference media (SDA).
    5. Incubate at (25 ± 1) °C for 5 days.
    6. Count the colonies on the medium under test (DG18) and the reference media (SDA).
    7. Calculate the productivity ratio PR. The criteria is: PR ≥ 0,5.
    8. If the PR exceeds 1,4 identify the reason.
    9. For this the total count of colonies obtained on the culture medium under test (DG18) is divided by the total count of colonies obtained on the defined reference medium (SDA).
    Calculate the productivity ratio PR as follows: PR  NS
    N0
    Ns = total count test medium
    N0 = total count reference medium

    Control strain WDCM number Ref. media Incubation Criteria Characteristic reaction
    Saccharomyces cerevisiae
    		SDA (25 ± 1) °C for 5 days PR ≥ 0,5 Characteristic colony/propagules according to each species
    + Wallemia sebi
    Aspergillus restrictus
    00183 opt
    Eurotium rubrum
    00184 opt
    The best practice for Quantitative control of Productivity for media control of 'DG18' is based on the data displayed in this table according ISO 11133.

  • Qualitative control of Selectivity

    • Best Practice DG18

    Qualitative control of Selectivity solid medium

    1. Use a reference material or test suspension with a known number of Escherichia coli and Bacillus subtilis subsp. spizizenii.
    2. Streak each test strain (Escherichia coli and Bacillus subtilis subsp. spizizenii) as a single line on the media under test (DG18).
    3. Multiple strains can be streaked on the plate as long no crossing occurs.
    4. Use a 1 µl loop in case of a concentration of at least 10000 cfu or a 10 µl loop in case of a concentration between 1000 and 10000 cfu.
    5. Incubate at (25 ± 1) °C for 5 days.
    6. Asses the amount of growth as, 0 for no growth, 1 for weak growth or 2 for good growth.
    7. For this medium (DG18) and standard (ISO 21527-2) combination the criteria is: "No Growth.

    Control strain WDCM number Ref. media Incubation Criteria Characteristic reaction
    Escherichia coli
    00012 opt
    		 (25 ± 1) °C for 5 days No Growth No Growth
    + Bacillus subtilis subsp. spizizenii
    The best practice for Qualitative control of Selectivity for media control of 'DG18' is based on the data displayed in this table according ISO 11133.