An Improved Enrichment Procedure for the Isolation of Yersinia enterocolitica and Related Species From Milk

A new enrichment procedure is proposed to improve the isolation of Yersinia enterocolitica and related species from milk. This procedure uses tryptic soy broth plus Polymyxin (5 IU/ml) and Novobiocin (10 μg/ml) - TSPN broth - incubated at 18°C for 3 d. Using raw milk and pasteurized milk inoculated with Yersinia strains, the efficiency of this procedure was compared to that of SB broth (sorbitol bile salts broth) incubated at 4°C for up to 21 d. Despite of the presence of antibiotics in TSPN broth, there were difficulties in recovering Yersinia from raw milk samples due to the presence of high levels of other organisms. Nevertheless, TSPN broth incubated at 18°C for 3 d showed better efficiency than the other method. In pasteurized milk samples, TSPN medium at 18°C for 3 d gave better results than the SB broth at 4°C for 7 d, showing that the proposed procedure is the preferable one due to the shorter period of incubation.