Trend of occurrence and serotypes in Sardinian pig slaughterhouses.

The aim of this study was to evaluate prevalence and serotypes in four Sardinian pig slaughterhouses. Moreover, a population study was conducted with pulsed field gel electrophoresis (PFGE). The results were compared with previous investigations carried out during years 2008 and 2014. A total of 147 samples were collected, 117 from slaughtered pigs (lymph nodes, colon content and carcass surface) and 30 from the slaughterhouse environment (surfaces in contact and not in contact with meat). was isolated from 3.4% pig samples and was not detected from environmental samples. Comparing the results with those of previous investigations, occurrence showed a sharp decrease through the years in both animals (18.8% in 2008, 10% in 2014 and 3.4% in 2020) and environmental samples (34.1% in 2008, 3.7 in 2014, and 0% in 2020). At the same time, prevalence of carriers (pigs positive at lymph nodes and/or colon content level) showed a reduction through the years and was always lower in animals coming from local farms rather than those coming from other European Member States, probably indicating the role of stressful factors as transport in increasing susceptibility and shedding. serotypes were monophasic Typhimurium, Rissen and Muenchen. Overall, 13 different serotypes were identified during the three surveys with the most prevalent being serotypes often isolated from slaughtered pigs and during human salmonellosis cases: Derby and . Typhimurium in 2008, Anatum and Rissen in 2014, monophasic Typhimurium in 2020. Population study with pulsed field gel electrophoresis showed a high similarity between strains belonging to the same serotype. The results of the investigations showed a decrease of occurrence during twelve years in Sardinia, probably due to the improvement in the application of correct GMPs and GHPs at slaughterhouse and also to a reduction of the rate of carrier pigs at farm level.