ISO 11731 (2017) medium: MWY

Media control Water quality 

Microorganisms and performance criteria for testing selective media 'MWY' for Enumeration of Legionella used in Water quality  microbiology by comparing with a non-selective reference medium according to ISO 11731.

  • 1 Quantitative control of Productivity

  • White-grey-blue-purple colonies with an entire edge and exhibiting a characteristic groundglass appearance. The characteristic reaction of  on MWY
    The characteristic reaction of Legionella pneumophila on MWY: White-grey-blue-purple colonies with an entire edge and exhibiting a characteristic groundglass appearance.

    Best Practice MWY

    Quantitative control of Productivity solid medium

    1. Use a quantitative reference material or test suspension with a known number of Legionella pneumophila.
    2. Dilute this material so 50 to 120 cfu is inoculated on the MWY.
    3. Use the same method of inoculation as described in the specific individual ISO 11731.
    4. Do this also for the reference media (BCYE).
    5. Incubate at (36 ± 2) °C for 2d to 5d.
    6. Count the colonies on the medium under test (MWY) and the reference media (BCYE).
    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 (MWY) is divided by the total count of colonies obtained on the defined reference medium (BCYE).
    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
    Legionella pneumophila BCYE (36 ± 2) °C for 2d to 5d PR ≥ 0,5 White-grey-blue-purple colonies with an entire edge and exhibiting a characteristic groundglass appearance
    The best practice for Quantitative control of Productivity for media control of 'MWY' is based on the data displayed in this table according ISO 11731.
  • 2 Quantitative control of Productivity opt

  • Best Practice MWY

    Quantitative control of Productivity solid medium

    1. Use a quantitative reference material or test suspension with a known number of Legionella anisa.
    2. Dilute this material so 50 to 120 cfu is inoculated on the MWY.
    3. Use the same method of inoculation as described in the specific individual ISO 11731.
    4. Do this also for the reference media (BCYE).
    5. Incubate at (36 ± 2) °C for 5d to 10d.
    6. Count the colonies on the medium under test (MWY) and the reference media (BCYE).
    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 (MWY) is divided by the total count of colonies obtained on the defined reference medium (BCYE).
    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
    Legionella anisa BCYE (36 ± 2) °C for 5d to 10d PR ≥ 0,5 White-grey-blue-purple colonies with an entire edge and exhibiting a characteristic groundglass appearance
    The best practice for Quantitative control of Productivity for media control of 'MWY' is based on the data displayed in this table according ISO 11731.
  • 1 Qualitative control of Selectivity

  • Best Practice MWY

    Qualitative control of Selectivity solid medium

    1. Use a reference material or test suspension with a known number of Enterococcus faecalis.
    2. Streak the test strain (Enterococcus faecalis) as a single line on the media under test (MWY).
    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 (36 ± 2) °C for 3d.
    5. Asses the amount of growth as, 0 for no growth, 1 for weak growth or 2 for good growth.
    6. For this medium (MWY) and standard (ISO 11731) combination the criteria is: "Total inhibition.

    Control strain WDCM number Ref. media Incubation Criteria Characteristic reaction
    Enterococcus faecalis or (36 ± 2) °C for 3d Total inhibition No growth
    The best practice for Qualitative control of Selectivity for media control of 'MWY' is based on the data displayed in this table according ISO 11731.
  • 2 Qualitative control of Selectivity

  • Best Practice MWY

    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 (MWY).
    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 (36 ± 2) °C for 3d.
    5. Asses the amount of growth as, 0 for no growth, 1 for weak growth or 2 for good growth.
    6. For this medium (MWY) and standard (ISO 11731) combination the criteria is: "Total inhibition (0 to 1)".

    Control strain WDCM number Ref. media Incubation Criteria Characteristic reaction
    Escherichia coli or (36 ± 2) °C for 3d Total inhibition (0 to 1) No growth
    The best practice for Qualitative control of Selectivity for media control of 'MWY' is based on the data displayed in this table according ISO 11731.