[Biochemical differentiation of Listeria from cheese]

Listeria spp. isolated from cheese were tested for biochemical characteristics together with reference strains from culture collections. Microtitration plates were used for testing the fermentation patterns. The results were subjected to a numerical cluster analysis based on linkage maps. The variation of the group structures calculating the characteristics with and without the hemolysin reactions is demonstrated. The pathogenic species L. monocytogenes could only be separated from the avirulent species L. innocua by the hemolysin tests. Most of the cheese isolates were identified as L. innocua, some as L. monocytogenes and L. seeligeri. There is a need for an inexpensive commercial test kit to identify the serovars or virulence factors of Listeria spp. in the quality assessment of food. The present study sets up doubts for a sufficiently ensured separation of L. innocua from L. monocytogenes.