CHROMagar Listeria Method

CHROMagar has developed a rapid method for the detection of Listeria monocytogenes in food stuff. L. monocytogenes is a widespread bacteria present in soil, sewage and faecal matter. Its ability to form listerial biofilms on contact surfaces makes it difficult to eliminate. This pathogen can cause serious food poisoning and is therefore frequently a microbial QC target in food processing facilities to avoid food contamination.

The method comprises the following steps: (1) enrichment in Half Fraser Broth for 24 h; (2) isolation in CHROMagar Listeria; (3) confirmation of L. monocytogenes species in CHROMagar Identification Listeria. This method was validated by the AFNOR, in comparison to the method described in the ISO-11290. This validation showed that the CHROMagar method had the same rate of detection, while dramatically reducing both the time to result and the workload.

Classical confirmatory tests for the L. monocytogenes species include many tedious and time-consuming steps (purification + catalase + haemolysis + dextrose + rhamnose + xylose ...). This method is far simpler - a single spot of a suspect colony out of CHROMagar Listeria directly put onto CHROMagar Identification Listeria will provide confirmation of L. monocytogenes species within 24 hours. Furthermore, the species will be easily differentiated from other Listeria directly at the isolation step: the colonies are blue and surrounded by a white halo due to a specific phospholipase activity.