Isolation of Salmonella enterica in pigs at slaughter and genetic identity between isolates of porcine and human origin in Northern Italy.

Introduction: Salmonella spp. is a zoonotic microorganism responsible for food-borne disease worldwide. Even if the EU-trend is decreasing, salmonellosis is still the second most common food-borne disease in the European Union and swine are considered an important reservoir of microorganisms for humans. Materials and Methods: From June to October 2014, 201 pigs at slaughter were tested for Salmonella spp. in mesenteric lymph nodes. Pigs were reared in 61 farms of four Italian regions (Lombardy, Emilia-Romagna, Veneto and Piedmont) and slaughtered in one abattoir in Emilia-Romagna region. A total of 67 batches of pigs were tested, and 3 animals per batch were randomly selected along the slaughter line. Prior to slaughter, 66 faecal samples were collected at lairage (two per sampling day). Salmonella spp. was detected following the ISO 6579:2002 method for lymph nodes and the ISO 6579/2002/Amd.1:2007 for faecal samples. Serotyping of isolates was performed following the Kauffmann White-Le Minor scheme. Genotyping was carried out by PFGE after digestion of DNA with the restriction enzyme XbaI according to the Pulse Net protocol. A total of around 3,000 Salmonella isolates from hospitalized human patients of Emilia-Romagna region were typed from October 2011 to October 2014. They were linked to several salmonellosis outbreaks or single cases. Results: Overall, 39 lymph nodes (19.4%) and 33 faecal samples (50.0%) were found positive for Salmonella. The following Salmonella serovars were detected, listed in order of frequency: S. Derby, S. enterica 1,4,[5],12:i:-, S. Rissen, S. Brandenburg, S. Manhattan, S. London, S. Livingstone, S. Muenchen, S. Stanley, S. Give. All serovars except S. Stanley were isolated from human cases of infections. Comparing PFGE profiles between the porcine and human compartments, the largest proportion of pulsotypes that were present in both compartments was observed among the isolates of S. enterica 1,4,[5],12:i:- (7 out of the 10 porcine pulsotypes were present in the human isolates) whereas the smallest proportion of shared pulsotypes was observed among the isolates of S. Derby (6 out of the 15 porcine pulsotypes were present in the human isolates). Interestingly, pulsotypes of S. enterica 1,4,[5],12:i:- isolated from pigs did not always correspond to S. enterica 1,4,[5],12:i:-isolates in the human compartment, instead, in some cases they correspond to the biphasic S. Typhimurium. Conclusions: This study confirms the role of pigs as pathogenic Salmonella strains for humans. Future studies will be necessary to acquire better knowledge on the ecology of S. Typhimurium and its monophasic variant between the porcine and human compartments, considering the importance of these serotypes in human salmonellosis.