Horizontal method for the detection and enumeration of Listeria monocytogenes and of Listeria spp. - Part 2: Enumeration method
Quantitative process control with CRM-LM
- Use a quantitative reference material (CRM-LM) with a known number of Listeria monocytogenes.
- Defrost the material at room temperature for 30 minutes.
- Mix well before use and dilute the material so countable numbers are inoculated on the media (ALOA) by spread plate method.
- Best results are obtained when a practicable range of 80 cfu to 120 cfu per plate with a minimum number of 50 cfu per plate is used.
- Incubate at (37 ± 1) °C for (48 ± 4) h.
- Count the colony forming units and register in a control chart.
- The characteristic reaction is: Blue green colonies with opaque halo.
The single strain CRM-LM is used for the enumeration of Listeria monocytogenes