Occurrence of Erysipelothrix spp., Salmonella spp., and Listeria spp. in tonsils of healthy Swiss pigs at slaughter

Healthy food producing animals were recognized in recent years as important carriers of bacterial pathogens causing human illness. To obtain microbiological data from Swiss pigs at slaughter, tonsils samples were examined in the present study for the occurrence of Erysipelothrix, Salmonella, and Listeria over a 3-month period. No Erysipelothrix spp. were found in 250 tonsil samples by culture after an enrichment step. Salmonella spp. were detected (ISO 6579:09.2006) in only 0.8 % (2/250) of the tonsils from the tested animals, corresponding to a batch prevalence of 1.4 %. The two isolates were identified as Salmonella Bredeney and Salmonella Kedougou, which are only rarely reported as cause of human illness. Listeria spp. were detected (ISO 11290-1:2004) in 5.6 % (14/250) of the tonsils from the tested animals, corresponding to a batch prevalence of 11.1 %. Of the 14 isolates, nine were identified as Listeria monocytogenes, four as Listeria ivanovii, and one as Listeria innocua. The Listeria monocytogenes strains belonged to the serotypes 1/2a, 1/2b, and 4b. Though numbers were low compared to the data from some other European countries, the present study shows that Salmonella and Listeria monocytogenes could be detected in the tonsils from healthy pigs at slaughter and these pathogens might pose a threat for the contamination of carcasses and the slaughterhouse environment.