ISO 11731 (2017) medium: BCYE+AB

Media control Water quality 

Microorganisms and performance criteria for testing selective media 'BCYE+AB' 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 BCYE+AB
    The characteristic reaction of Legionella pneumophila on BCYE+AB: White-grey-blue-purple colonies with an entire edge and exhibiting a characteristic groundglass appearance.

    Best Practice BCYE+AB

    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 BCYE+AB.
    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 (BCYE+AB) 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 (BCYE+AB) 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 'BCYE+AB' is based on the data displayed in this table according ISO 11731.
  • 2 Quantitative control of Productivity opt

  • Best Practice BCYE+AB

    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 BCYE+AB.
    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 (BCYE+AB) 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 (BCYE+AB) 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 'BCYE+AB' is based on the data displayed in this table according ISO 11731.
  • 1 Qualitative control of Selectivity

  • Best Practice BCYE+AB

    In practice it turns out that Enterococcus faecalis is able to form colonies on BCYE + AB. The antibiotic that causes inhibition of the growth of Enterococcus faecalis strains is vancomycin. This antibiotic is present in MWY and GVPC but not in BCYE+AB

    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 (BCYE+AB).
    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 (BCYE+AB) 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 'BCYE+AB' is based on the data displayed in this table according ISO 11731.
  • 2 Qualitative control of Selectivity

  • Best Practice BCYE+AB

    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 (BCYE+AB).
    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 (BCYE+AB) 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 'BCYE+AB' is based on the data displayed in this table according ISO 11731.