Microorganisms and performance criteria for testing selective media 'TBX' for Enumeration of β-d- Glucuronidasepositive Escherichia coli used in Food chain microbiology according to ISO 11133.
ISO 16649-1 (2018) medium: TBX
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Quantitative control of Productivity
- Use a quantitative reference material or test suspension with a known number of Escherichia coli.
- Dilute this material so 50 to 120 cfu is inoculated on the TBX by pouring for example 1 mL.
- Do this also for the reference media (TSA).
- Incubate at (44 ± 1) °C for (21 ± 3) h.
- Count the colonies on the medium under test (TBX) and the reference media (TSA).
- Calculate the productivity ratio PR. The criteria is: PR ≥ 0,5.
- If the PR exceeds 1,4 identify the reason.
- For this the total count of colonies obtained on the culture medium under test (TBX) is divided by the total count of colonies obtained on the defined reference medium (TSA).
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Qualitative control of Selectivity
- 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 (TBX).
- 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 (44 ± 1) °C for (21 ± 3) h.
- Asses the amount of growth as, 0 for no growth, 1 for weak growth or 2 for good growth.
- For this medium (TBX) and standard (ISO 16649-1) combination the criteria is: "Total inhibition (0).
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Qualitative control of Specificity
- Use a reference material or test suspension with a known number of Citrobacter freundii.
- Streak each test controlstrain (Citrobacter freundii) on the media under test (TBX) to obtain discrete colonies.
- Use a 1 µl loop in case of a concentration of at least 1000 cfu/mL.
- Incubate at (44 ± 1) °C for (21 ± 3) h.
- Asses the presence, absence and/or grade of expression of biochemical responses and colony sizes and morphology.
- For this medium (TBX) and standard (ISO 16649-1) combination the characteristic reaction is: White to green-beige colonies.
Best Practice TBX
Quantitative control of Productivity solid medium
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 |
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Escherichia coli | TSA | (44 ± 1) °C for (21 ± 3) h | PR ≥ 0,5 | Blue colonies | |
The best practice for Quantitative control of Productivity for media control of 'TBX' is based on the data displayed in this table according ISO 11133. |
Best Practice TBX
Qualitative control of Selectivity solid medium
Control strain | WDCM number | Ref. media | Incubation | Criteria | Characteristic reaction |
---|---|---|---|---|---|
Enterococcus faecalis | or | (44 ± 1) °C for (21 ± 3) h | Total inhibition (0) | No growth | |
The best practice for Qualitative control of Selectivity for media control of 'TBX' is based on the data displayed in this table according ISO 11133. |
Best Practice TBX
Qualitative control of Specificity solid medium
Control strain | WDCM number | Ref. media | Incubation | Criteria | Characteristic reaction |
---|---|---|---|---|---|
Citrobacter freundii | (44 ± 1) °C for (21 ± 3) h | growth | White to green-beige colonies | ||
Pseudomonas aeruginosa | |||||
The best practice for Qualitative control of Specificity for media control of 'TBX' is based on the data displayed in this table according ISO 11133. |