Serodiversity and serological as well as cultural distribution of Salmonella on farms and in abattoirs in Lower Saxony, Germany

Abstract

In this study fattening pigs were monitored on farms and in the abattoir for Salmonella prevalence. The samples with the highest prevalence at slaughter should be identified with special attention to the distribution of Salmonella serovars on farms in comparison to those in slaughtered pigs. Another aim was to monitor whether high serological antibody responses in pigs are in accordance with the specific Salmonella serovars in tissues. From 3418 farm faecal samples, 191 were Salmonella positive (5.58%), whereas from slaughtered pigs 330 out of 2494 analysed samples were Salmonella positive (13.2%) with the highest prevalence in the caecal content (124/499=24.9%). The chi-square test for homogeneity between the serovars found on farms and in the different types of samples at slaughter was in most cases negative (p<0.05). Exceptions were the similar serovars found in samples taken from farm 1 and in the corresponding ileocaecal lymph nodes extracted at slaughter (p=0.1188); in samples taken from farm 2 and the corresponding tonsils (p=0.1479) and in samples taken from farm 3 and the corresponding caecal content (p=0.3230) and ileocaecal lymph nodes (p=0.1921), respectively. The frequency distribution in different samples was significantly different in most cases. Three exceptions, the distribution between tonsils and caecal content among antibody titre in meat juice (cut off 40) and cultural detection of Salmonella spp. in ileocaecal lymph nodes, as well as between meat juice samples (cut off 20) and caecal content did not differ significantly. The Kappa indices only showed signs of weak concordance according to positive test results (Kappa ≤ 0.4) between different sample types on an animal basis. Pigs harbouring S. Typhimurium 1,4,12:i:1,2; DT104L in tonsils or S. Typhimurium 1,4,12:i:1,2 DT 104B low in caecal content or ileocaecal lymph nodes had the highest optical densities in meat juice. Apart from the different Salmonella prevalences between farms and slaughterhouses and in most cases non-existing concordance in Salmonella serovar distribution on farms and at slaughter, also in future farm intervention strategies to control Salmonella in the food chain are not dispensable. This is because once introduced into a slaughterhouse via swine the serovars seem to maintain the resident slaughterhouse flora and add to it.