Microorganisms and performance criteria for non-selective liquid media 'Peptone diluent' used in Water quality microbiology according to ISO 11133.
Quantitative control of Dilution
- Use a reference material or test suspension with a known number of Staphylococcus aureus.
- Inoculate a test portion (e.g. 9 mL) of the diluent with 1 mL of the test microorganism (Dilution liquids) 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 °C – 25 °C)) for ((45 min – 1 h)).
- 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 Peptone diluent
|Control strain||WDCM number||Ref. media||Incubation||Criteria||Characteristic reaction|
|Staphylococcus aureus||TSA||(20 °C – 25 °C) for (45 min – 1 h)||+/- 30 % colonies/ T0 (+/- 30 % of original count)||No characteristic colonies|
|The best practice for Quantitative control of Dilution for media control of 'Peptone diluent' is based on the data displayed in this table according ISO 11133.|