INACTIVATION OF YERSINIA ENTEROCOLITICA BY THE LACTOPEROXIDASE SYSTEMIN A SEMISYNTHETIC MEDIUM AND IN RAW-MILK

A semi-synthetic medium (SSM) and raw milk were inoculated to contain Yersinia enterocolitica strain 2635 NT at ca. 10(4) or ca. 10(8) cfu/m l. The lactoperoxidase system (LPS) reduced numbers of Y. enterocoliti ca after 2 h at 4-degrees-C when SSM or raw milk initially contained 1 0(4) cfu/ml. Numbers continued to decrease and the maximum reduction o ccurred after 5 d of incubation (7.3 and 4.8 orders of magnitude diffe rence between treated and untreated samples for SSM and raw milk, resp ectively). When the initial population was 10(8) cfu/ml, the LPS reduc ed numbers of the pathogen by 3.4 and 2.8 orders of magnitude (when co mpared to controls) in SSM and raw milk, respectively, after 5 d at 4- degrees-C. At 30-degrees-C, the LPS caused both initial populations of Y. enterocolitica in SSM to decrease within 2 h with maximum inactiva tion occurring after 12 h; for large and small initial populations it was ca. 3.5 and 6.5 orders of magnitude (when compared to controls), r espectively. In raw milk at 30-degrees-C, maximum reduction also occur red after 12 h of incubation (5.4 and 5.0 orders of magnitude when com pared to controls for the small and large initial populations, respect ively). The decrease at 30-degrees-C in SSM and raw milk was followed by growth of surviving cells. Generally, the degree to which Y. entero colitica was inactivated by the LPS was related to initial population of the pathogen, time of exposure to the LPS, and incubation temperatu re. The LPS may be useful to temporarily control Y. enterocolitica in raw milk and this could be beneficial from a public health viewpoint.