ISO 6888-2 (1999) medium: RPFA

Media control Food and animal feeding stuffs

Microorganisms and performance criteria for testing selective media 'RPFA' for Enumeration of Coagulase-positive staphylococci used in Food and animal feeding stuffs microbiology according to ISO 11133.

  • Quantitative control of Productivity

  • Black or grey colonies with opacity halo. The characteristic reaction of  on RPFA
    The characteristic reaction of Staphylococcus aureus on RPFA: Black or grey colonies with opacity halo.

    Best Practice RPFA

    Quantitative control of Productivity solid medium

    1. Use a quantitative reference material or test suspension with a known number of Staphylococcus aureus.
    2. Dilute this material so 50 to 120 cfu is inoculated on the RPFA 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 to (48 ± 2) h.
    5. Count the colonies on the medium under test (RPFA) 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 (RPFA) 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
    Staphylococcus aureus TSA (37 ± 1) °C for (24 ± 2) h to (48 ± 2) h PR ≥ 0,5 Black or grey colonies with opacity halo
    The best practice for Quantitative control of Productivity for media control of 'RPFA' is based on the data displayed in this table according ISO 11133.
  • Qualitative control of Selectivity

  • Best Practice RPFA

    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 (RPFA).
    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 (48 ± 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 (RPFA) and standard (ISO 6888-2) combination the criteria is: "Total inhibition (0).

    Control strain WDCM number Ref. media Incubation Criteria Characteristic reaction
    Escherichia coli or (37 ± 1) °C for (48 ± 2) h Total inhibition (0) No growth
    The best practice for Qualitative control of Selectivity for media control of 'RPFA' is based on the data displayed in this table according ISO 11133.
  • Qualitative control of Specificity

  • Best Practice RPFA

    Qualitative control of Specificity solid medium

    1. Use a reference material or test suspension with a known number of Staphylococcus saprophyticus.
    2. Streak the test controlstrain (Staphylococcus saprophyticus) on the media under test (RPFA) to obtain discrete colonies.
    3. Use a 1 µl loop in case of a concentration of at least 1000 cfu/mL.
    4. Incubate at (37 ± 1) °C for (24 ± 2) h to (48 ± 2) h.
    5. Asses the presence, absence and/or grade of expression of biochemical responses and colony sizes and morphology.
    6. For this medium (RPFA) and standard (ISO 6888-2) combination the characteristic reaction is: Black or grey colonies without opacity halo.

    Control strain WDCM number Ref. media Incubation Criteria Characteristic reaction
    Staphylococcus saprophyticus (37 ± 1) °C for (24 ± 2) h to (48 ± 2) h growth Black or grey colonies without opacity halo
    Staphylococcus epidermidis
    The best practice for Qualitative control of Specificity for media control of 'RPFA' is based on the data displayed in this table according ISO 11133.