Listeria monocytogenes: diagnostic problems.

The first isolation methods for the detection of Listeria spp. were generally based on the direct culture of samples on simple agar media, but isolation of the pathogenic Listeria monocytogenes was difficult. In time, new techniques were developed, based on a variety of selective and elective agents in isolation and enrichment media, which gained better and quicker results. Current reference methods allow the recovery of L. monocytogenes from a variety of foods with relative ease. However, more comparative studies are needed to select one horizontal method. It is suggested that the procedure of the International Organization for Standardization is a good base for such comparisons.