Method for detection and numeration of Listeria monocytogenes

Dutec Diagnostics has announced its rapid method for the detection of Listeria monocytogenes in food, the CHROMagar Listeria method, using CHROMagar Listeria, then CHROMagar Identification Listeria.

According to the company, the method requires three steps. First, enrichment in half frazer broth for 24 hours, then isolation in CHROMagar Listeria and, finally, confirmation of L. monocytogenes species in CHROMagar Identificiation Listeria.

This method was validated by the AFNOR, in comparison to the method described in the ISO-11290. The company claims this validation showed that the CHROMagar Listeria method had the same rate of detection as the classical method, but reduced both the time to result and the workload.

CHROMagar Listeria is suitable for detection and numeration of L. monocytogenes. Since L. monocytogenes and L. innocua have similar biochemical properties, they cannot be differentiated on traditional media. CHROMagar Listeria helps to differentiate L. monocytogenes from other Listeria directly at the isolation step: the colonies are blue and surrounded by a white halo due to a specific phospholipase activity.

For confirmation of L. monocytogenes species from suspect colonies on CHROMagar Listeria, CHROMagar Identification Listeria is required. Classical confirmatory tests for the L. monocytogenes species can include many steps. This method can simplify the species confirmatory step and reduce the workload. A single spot of a suspect colony out of CHROMagar Listeria put directly onto CHROMagar Identification Listeria will provide confirmation of L. monocytogenes species within 24 hours, claims Dutec.