(BioMed Central, 2014) Garrido González, Victoria; Sánchez Alarcón, Samanta Rita; San Román Aberasturi, Beatriz; Zabalza Baranguá, Ana; Díaz Tendero, Yasmín; Frutos, Cristina de; Mainar Jaime, Raúl Carlos; Grilló Dolset, María Jesús; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua; Gobierno de Navarra / Nafarroako Gobernua: IIQ14064.RI1; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Background: Salmonellosis is a major worldwide zoonosis, and Salmonella-infected finishing pigs are considered
one of the major sources of human infections in developed countries. Baseline studies on salmonellosis prevalence
in fattening pigs in Europe are based on direct pathogen isolation from mesenteric lymph nodes (MLN). This
procedure is considered the most reliable for diagnosing salmonellosis in apparently healthy pigs. The presence of
simultaneous infections by different Salmonella strains in the same animal has never been reported and could have
important epidemiological implications.
Results: Fourteen finishing pigs belonging to 14 farms that showed high salmonellosis prevalence and a variety of
circulating Salmonella strains, were found infected by Salmonella spp, and 7 of them were simultaneously infected
with strains of 2 or 3 different serotypes. Typhimurium isolates showing resistance to several antimicrobials and
carrying mobile integrons were the most frequently identified in the colonized MLN. Four animals were found
infected by Salmonella spp. of a single serotype (Rissen or Derby) but showing 2 or 3 different antimicrobial
resistance profiles, without evidence of mobile genetic element exchange in vivo.
Conclusion: This is the first report clearly demonstrating that pigs naturally infected by Salmonella may harbour
different Salmonella strains simultaneously. This may have implications in the interpretation of results from baseline
studies, and also help to better understand human salmonellosis outbreaks and the horizontal transmission of
antimicrobial resistance genes.
