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Open Access Research article

Simultaneous infections by different Salmonella strains in mesenteric lymph nodes of finishing pigs

Victoria Garrido1, Samanta Sánchez1, Beatriz San Román1, Ana Zabalza-Baranguá1, Yasmin Díaz-Tendero2, Cristina de Frutos2, Raúl-Carlos Mainar-Jaime3 and María-Jesús Grilló1*

Author Affiliations

1 Animal Health, Instituto de Agrobiotecnología (CSIC-UPNA-Gobierno de Navarra), Pamplona, Spain

2 Central Veterinary Laboratory, MAGRAMA, Madrid, Spain

3 Departamento de Patología Animal, Facultad de Veterinaria, Universidad de Zaragoza, Zaragoza, Spain

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BMC Veterinary Research 2014, 10:59  doi:10.1186/1746-6148-10-59

Published: 7 March 2014

Abstract

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.

Keywords:
Salmonella; Multiple infections; Pigs; Serotypes; Antimicrobial resistance