Wystepowanie Listeria monocytogenes w mleku surowym i produktach mlecznych

Studies were carried out on 134 samples of raw milk originating from small farms and 87 samples of raw milk collected from a large dairy farm. Moreover, 73 samples of pasteurized milk and 44 samples of cheese, cream, ice-cream and yoghurt were assessed for the presence of L. monocytogenes. The detection of Listeria sp. in 25 ml (or g) per milk or dairy product samples was performed according to the IDF method. L. monocytogenes was isolated from 2 (1.75 per cent) of the 134 samples of raw milk samples coming from individual farms. Out of 16 dairy farm-bulk raw milk samples 9 (56.2 per cent) were positive in relation to L. monocytogenes. In the case of quarter milk, only 6 (7.4 per cent) out of 81 was infected with the pathogen. L. monocytogenes was not found in any milk product. Altogether 17 virulent strains of L. monocytogenes were isolated from the materials under study. It was shown by the slide agglutination test that all the isolated strains belonged to serotype 1. In addition, 21 apathogenic strains were isolated and among them eight were classified as L. innocua.