ISO 19250 (2013) medium: XLD

Media control Water quality 

Microorganisms and performance criteria for selective isolation media 'XLD' used in Water quality  microbiology according to ISO 11133.

  • Qualitative control of Productivity

    • Best Practice XLD

    Qualitative control of Productivity solid medium

    1. Use a reference material or test suspension with a known number of Salmonella Typhimurium and Salmonella Enteritidis.
    2. The volume used for testing should contain 103 to 104 cfu for qualitative tests of plate media.
    3. Streak each test microorganism (Salmonella Typhimurium and Salmonella Enteritidis) on the media under test (XLD) to obtain discrete colonies.
    4. Incubate at (36 ± 2) °C for (24 ± 3) 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 (XLD) and standard (ISO 19250) combination the criteria is: "Good growth (2)".
    7. The Characterictic reaction is: Colonies with black centre and a lightly transparent zone of reddish colour due to the colour change of the medium.

    Control strain WDCM number Incubation Criteria Characteristic reaction
    Salmonella Typhimurium
    		(36 ± 2) °C for (24 ± 3) h Good growth (2) Colonies with black centre and a lightly transparent zone of reddish colour due to the colour change of the medium
    + Salmonella Enteritidis
    The best practice for Qualitative control of Productivity for media control of 'XLD' is based on the data displayed in this table according ISO 11133.

  • 1 Qualitative control of Selectivity man

    • Best Practice XLD

    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 (XLD).
    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 (24 ± 3) 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 (XLD) and standard (ISO 19250) combination the criteria is: "Growth or partial inhibition (0−1).

    Control strain WDCM number Ref. media Incubation Criteria Characteristic reaction
    Escherichia coli
    or
    		(36 ± 2) °C for (24 ± 3) h Growth or partial inhibition (0−1) Yellow colonies
    The best practice for Qualitative control of Selectivity for media control of 'XLD' is based on the data displayed in this table according ISO 11133.

  • 2 Qualitative control of Selectivity man

    • Best Practice XLD

    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 (XLD).
    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 (24 ± 3) 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 (XLD) and standard (ISO 19250) combination the criteria is: "Total inhibition (0)".

    Control strain WDCM number Ref. media Incubation Criteria Characteristic reaction
    Enterococcus faecalis
    or
    		(36 ± 2) °C for (24 ± 3) h Total inhibition (0) No growth
    The best practice for Qualitative control of Selectivity for media control of 'XLD' is based on the data displayed in this table according ISO 11133.