ISO 7932 (2004) medium: MYP

Media control Food and animal feeding stuffs

Microorganisms and performance criteria for testing selective media 'MYP' for Enumeration of Bacillus cereus used in Food and animal feeding stuffs microbiology according to ISO 11133.

  • Quantitative control of Productivity

  • Pink colonies with precipitation halo. The characteristic reaction of  on MYP
    The characteristic reaction of Bacillus cereus on MYP: Pink colonies with precipitation halo.

    Best Practice MYP

    Quantitative control of Productivity solid medium

    1. Use a quantitative reference material or test suspension with a known number of Bacillus cereus.
    2. Dilute this material so 50 to 120 cfu is inoculated on the MYP by spreading for example 0.1 mL.
    3. Do this also for the reference media (TSA).
    4. Incubate at (30 ± 1) °C for (24 ± 3) h to (44 ± 4) h.
    5. Count the colonies on the medium under test (MYP) and the reference media (TSA).
    6. Calculate the productivity ratio PR. The criteria is: PR ≥ 0,5.
    7. If the PR exceeds 1,4 identify the reason.
    8. For this the total count of colonies obtained on the culture medium under test (MYP) is divided by the total count of colonies obtained on the defined reference medium (TSA).
    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
    Bacillus cereus TSA (30 ± 1) °C for (24 ± 3) h to (44 ± 4) h PR ≥ 0,5 Pink colonies with precipitation halo
    The best practice for Quantitative control of Productivity for media control of 'MYP' is based on the data displayed in this table according ISO 11133.
  • Qualitative control of Selectivity

  • Best Practice MYP

    Qualitative control of Selectivity solid medium

    1. Use a reference material or test suspension with a known number of Escherichia coli.
    2. Streak the test strain (Escherichia coli) as a single line on the media under test (MYP).
    3. 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.
    4. Incubate at (30 ± 1) °C for (44 ± 4) h.
    5. Asses the amount of growth as, 0 for no growth, 1 for weak growth or 2 for good growth.
    6. For this medium (MYP) and standard (ISO 7932) combination the criteria is: "Total inhibition (0).

    Control strain WDCM number Ref. media Incubation Criteria Characteristic reaction
    Escherichia coli or (30 ± 1) °C for (44 ± 4) h Total inhibition (0) No growth
    The best practice for Qualitative control of Selectivity for media control of 'MYP' is based on the data displayed in this table according ISO 11133.
  • Qualitative control of Specificity

  • Yellow colonies without precipitation halo. The characteristic reaction of  on MYP
    The characteristic reaction of Bacillus subtilis subsp. spizizenii on MYP: Yellow colonies without precipitation halo.

    Best Practice MYP

    Qualitative control of Specificity solid medium

    1. Use a reference material or test suspension with a known number of Bacillus subtilis subsp. spizizenii.
    2. Streak the test controlstrain (Bacillus subtilis subsp. spizizenii) on the media under test (MYP) to obtain discrete colonies.
    3. Use a 1 µl loop in case of a concentration of at least 1000 cfu/mL.
    4. Incubate at (30 ± 1) °C for (44 ± 4) h.
    5. Asses the presence, absence and/or grade of expression of biochemical responses and colony sizes and morphology.
    6. For this medium (MYP) and standard (ISO 7932) combination the characteristic reaction is: Yellow colonies without precipitation halo.

    Control strain WDCM number Ref. media Incubation Criteria Characteristic reaction
    Bacillus subtilis subsp. spizizenii (30 ± 1) °C for (44 ± 4) h growth Yellow colonies without precipitation halo
    The best practice for Qualitative control of Specificity for media control of 'MYP' is based on the data displayed in this table according ISO 11133.