ISO 4832 (2006) medium: VRBL

Media control Food and animal feeding stuffs

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

  • Quantitative control of Productivity

  • Purplish-red colonies with or without precipitation halo. The characteristic reaction of  on VRBL
    The characteristic reaction of Escherichia coli on VRBL: Purplish-red colonies with or without precipitation halo.

    Best Practice VRBL

    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 VRBL by pouring for example 1 mL.
    3. Do this also for the reference media (TSA).
    4. Incubate at (30 ± 1) °C for (24 ± 2) h.
    5. Count the colonies on the medium under test (VRBL) and the reference media (TSA).
    6. Calculate the productivity ratio PR. The criteria is: PR ≥ 0,7.
    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 (VRBL) 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 (30 ± 1) °C for (24 ± 2) h PR ≥ 0,7 Purplish-red colonies with or without precipitation halo
    The best practice for Quantitative control of Productivity for media control of 'VRBL' is based on the data displayed in this table according ISO 11133.
  • Qualitative control of Selectivity

  • Best Practice VRBL

    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 (VRBL).
    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 (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 (VRBL) and standard (ISO 4832) combination the criteria is: "Total inhibition (0).

    Control strain WDCM number Ref. media Incubation Criteria Characteristic reaction
    Enterococcus faecalis or (30 ± 1) °C for (24 ± 2) h Total inhibition (0) No growth
    The best practice for Qualitative control of Selectivity for media control of 'VRBL' is based on the data displayed in this table according ISO 11133.
  • Qualitative control of Specificity

  • Best Practice VRBL

    Qualitative control of Specificity solid medium

    1. Use a reference material or test suspension with a known number of Pseudomonas aeruginosa.
    2. Streak the test controlstrain (Pseudomonas aeruginosa) on the media under test (VRBL) 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 (24 ± 2) h.
    5. Asses the presence, absence and/or grade of expression of biochemical responses and colony sizes and morphology.
    6. For this medium (VRBL) and standard (ISO 4832) combination the characteristic reaction is: Colourless to beige colonies.

    Control strain WDCM number Ref. media Incubation Criteria Characteristic reaction
    Pseudomonas aeruginosa (30 ± 1) °C for (24 ± 2) h Growth Colourless to beige colonies
    The best practice for Qualitative control of Specificity for media control of 'VRBL' is based on the data displayed in this table according ISO 11133.