Microorganisms and performance criteria for selective isolation media 'XLD' used in Water quality microbiology according to ISO 11133.
ISO 19250 (2013) medium: XLD
-
Qualitative control of Productivity
- Use a reference material or test suspension with a known number of Salmonella Typhimurium and Salmonella Enteritidis.
- The volume used for testing should contain 103 to 104 cfu for qualitative tests of plate media.
- Streak each test microorganism (Salmonella Typhimurium and Salmonella Enteritidis) on the media under test (XLD) to obtain discrete colonies.
- Incubate at (36 ± 2) °C for (24 ± 3) h.
- Asses the amount of growth as, 0 for no growth, 1 for weak growth or 2 for good growth.
- For this medium (XLD) and standard (ISO 19250) combination the criteria is: "Good growth (2)".
- The Characterictic reaction is: Colonies with black centre and a lightly transparent zone of reddish colour due to the colour change of the medium.
-
1 Qualitative control of Selectivity man
- Use a reference material or test suspension with a known number of Escherichia coli.
- Streak the test strain (Escherichia coli) as a single line on the media under test (XLD).
- 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.
- Incubate at (36 ± 2) °C for (24 ± 3) h.
- Asses the amount of growth as, 0 for no growth, 1 for weak growth or 2 for good growth.
- For this medium (XLD) and standard (ISO 19250) combination the criteria is: "Growth or partial inhibition (0−1).
-
2 Qualitative control of Selectivity man
- Use a reference material or test suspension with a known number of Enterococcus faecalis.
- Streak the test strain (Enterococcus faecalis) as a single line on the media under test (XLD).
- 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.
- Incubate at (36 ± 2) °C for (24 ± 3) h.
- Asses the amount of growth as, 0 for no growth, 1 for weak growth or 2 for good growth.
- For this medium (XLD) and standard (ISO 19250) combination the criteria is: "Total inhibition (0)".
Best Practice XLD
Qualitative control of Productivity solid 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. |
Best Practice XLD
Qualitative control of Selectivity solid medium
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. |
Best Practice XLD
Qualitative control of Selectivity solid medium
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. |