Microorganisms and performance criteria for multipurpose media 'BPW' used in Food chain microbiology according to ISO 11133.
Qualitative control of Dilution
- Use a reference material or test suspension with a known number of Listeria monocytogenes 4b.
- Inoculate a test portion (e.g. 9 mL) of the diluent with 1 mL of the test microorganism (Listeria monocytogenes) suspension containing around 104 cfu/mL and mix;
- Immediately remove 0,1 mL of inoculated diluent and spread over the surface of a non-selective agar (reference medium) such as TSA (t0).
- Hold the inoculated diluent at ambient temperature for 45 min.
- Mix and then remove the same volume (0,1 mL) and plate again on the reference medium (t1).
- Incubate at ((20 ± 2) °C) for ((1 h ± 5°min)).
- Count the colonies on the plates t0 and t1. The number of microorganisms at t1, shall be within ± 30 % of the initial count (t0).
Best Practice BPW
|Control strain||WDCM number||Ref. media||Incubation||Criteria||Characteristic reaction|
|Listeria monocytogenes 4b||TSA||(20 ± 2) °C for (1 h ± 5°min)||±30 % colonies/ T0 (±30 % of original count)||No characteristic colonies|
|Listeria monocytogenes 1/2a|
|The best practice for Qualitative control of Dilution for media control of 'BPW' is based on the data displayed in this table according ISO 11133.|