ISO 21528-2 (2017) medium: VRBG

Media control Food chain

Microorganisms and performance criteria for testing selective media 'VRBG' for Enumeration of Enterobacteriaceae used in Food chain microbiology according to ISO 21528-2.

  • Quantitative control of Productivity

  • Pink to red colonies with or without precipitation halo. The characteristic reaction of  on VRBG
    The characteristic reaction of Escherichia coli on VRBG: Pink to red colonies with or without precipitation halo.

    Best Practice VRBG

    Quantitative control of Productivity solid medium

    1. Use a quantitative reference material or test suspension with a known number of Escherichia coli.
    2. Dilute this material so 50 to 120 cfu is inoculated on the VRBG by pouring for example 1 mL.
    3. Do this also for the reference media (TSA).
    4. Incubate at (37 ± 1) °C for (24 ± 2) h.
    5. Count the colonies on the medium under test (VRBG) 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 (VRBG) 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
    Escherichia coli TSA (37 ± 1) °C for (24 ± 2) h PR ≥ 0,5 Pink to red colonies with or without precipitation halo
    Salmonella Typhimurium
    Salmonella Enteritidis
    The best practice for Quantitative control of Productivity for media control of 'VRBG' is based on the data displayed in this table according ISO 21528-2.
  • Qualitative control of Selectivity

  • Best Practice VRBG

    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 (VRBG).
    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 (37 ± 1) °C for (24 ± 2) 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 (VRBG) and standard (ISO 21528-2) combination the criteria is: "Total inhibition (0).

    Control strain WDCM number Ref. media Incubation Criteria Characteristic reaction
    Enterococcus faecalis or (37 ± 1) °C for (24 ± 2) h Total inhibition (0) No growth
    The best practice for Qualitative control of Selectivity for media control of 'VRBG' is based on the data displayed in this table according ISO 21528-2.