EFFECT OF SAMPLING PROCEDURE AND STRAIN VARIATION IN LISTERIA-MONOCYTOGENES ON THE DISCRIMINATION OF SPECIES IN THE GENUS LISTERIA BY FOURIER-TRANSFORM INFRARED-SPECTROSCOPY AND CANONICAL VARIATES ANALYSIS

The ability to discriminate successfully among cultures of all species of the Listeria genus by infrared spectroscopy in combination with ca nonical variate analysis was confirmed. The robustness of the method w as demonstrated by showing that the separation of L. monocytogenes and L. grayi was hardly affected by variations in broth medium, incubatio n temperature, incubation time and cell washing procedure. Discriminat ion among 24 strains of L. monocytogenes according to serotype allowed two groups to be recognised, one comprising serotypes 4 and 4b and th e other containing serotypes 1, 1/2b and 1/2c. When strain variation w as included in the species discrimination model, the classification of all the L. monocytogenes strains was virtually 100% correct.