Influencia de la alimentación en la presencia de Salmonella y composición del microbioma intestinal en porcino extensivo

Salmonellosis is the second most common zoonosis in the EU and pigs are, after birds, the second most important source of infection for humans. Therefore, swine salmonellosis is a serious public health problem that requires special monitoring and surveillance. To preserve consumers’ health, the EU recommended thorough checks at all stages of the food chain "from farm to table" with the intention of gradually reduce the bacterial load to reach food. Among other measures, it is planned to establish restrictions on international trade of pigs and their products to those countries that do not meet the objective of reducing prevalence. These restrictions can have major economic impact on our country, since the pig sector is a key pillar of livestock resources of Spain, which is the fourth largest producer after the US, China and Germany. Also, extensive pig like Basatxerri in Basque Country and northern Navarre is gaining importance as quality production and as a standard for sustainable rural development and animal welfare. However, epidemiological and health situation of salmonellosis in these animals is unknown. In this study, the presence of Salmonella spp. was analyzed in the intestinal content of a representative Basatxerri pig population and so the risk factors associated. Moreover, to assess the possible implication of dietary factors as a source of direct or indirect exclusion of Salmonella, the microbiome study was performed using massive sequencing of intestinal contents. As a result, Salmonella was isolated in 32.2 per cent of the animals and in 83.3 per cent of the analyzed farms, observing large differences in prevalence between farms. The isolates mainly belonged to the monophasic variant of S. Typhimurium (79.3 per cent) and S. Bovismorbificans (10.3 per cent), showing resistance to at least one (89.7 per cent) or more than two (86,2 per cent) of the antimicrobial analyzed, sulfisoxazole and streptomycin being the most important. Univariate analysis identified four risk factors directly related to the presence of Salmonella in the intestinal contents, which were: the number of animals per farm; the feed’s composition; the type of vegetation eaten by the animals; and the silos’ cleaning and disinfection. The last three parameters showed an association between each other, so the multivariate analysis was performed considering the composition of the feed as the most interesting associated factor, identifying the administration of feed as a risk factor (p equal to 0.008) of salmonellosis. To determine the relative weight of the other associated variables, it would be necessary to conduct a proper follow-up study to this objective. The study of intestinal microbiome revealed clear differences between the bacterial populations of positive and negative animals to Salmonella, and it was detected in the first group of animals an increase of the phylum Firmicutes and Proteobacteria, followed by a decrease of Bacteroides phylum. The comparison between the OTUs indicated the existence of differences in ten bacterial families among positive and negative pigs to Salmonella, with greater statistical weight Mycoplasmataceae, Enterobacteriaceae, Pseudomonadaceae and Verrucomicrobiaceae. To sum up, the results indicated that all animal feed (ie. feed composition and - or the additional vegetation consumed) is a risk factor of first importance in the prevalence of swine salmonellosis in extensive farms, which can be used as a tool for sustainable control of this important zoonosis from the farm.