title: Simultaneous infections by different Salmonella strains in mesenteric lymph nodes of finishing pigs.
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.
  
  
  CONCLUSIONS
  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.
authors.forename: Victoria
authors.initials: V
authors.lastname: Garrido
authors.forename: Samanta
authors.initials: S
authors.lastname: Sánchez
authors.forename: Beatriz
authors.initials: B
authors.lastname: San Román
authors.forename: Ana
authors.initials: A
authors.lastname: Zabalza-Baranguá
authors.forename: Yasmin
authors.initials: Y
authors.lastname: Díaz-Tendero
authors.forename: Cristina
authors.initials: C
authors.lastname: de Frutos
authors.forename: Raúl-Carlos
authors.initials: RC
authors.lastname: Mainar-Jaime
authors.affiliation: Animal Health, Instituto de Agrobiotecnología (CSIC-UPNA-Gobierno de Navarra), Pamplona, Spain. mariajesus.grillo@unavarra.es.
authors.forename: María-Jesús
authors.initials: MJ
authors.lastname: Grilló
mesh_terms: D000818:Animals; D052978:Disk Diffusion Antimicrobial Tests / Q000662:veterinary; D024881:Drug Resistance, Bacterial; D008198:Lymph Nodes / Q000382:microbiology; D008206:Lymphatic Diseases / Q000382:microbiology*; D008643:Mesentery / Q000382:microbiology; D012475:Salmonella / Q000187:drug effects; D012481:Salmonella Infections, Animal / Q000382:microbiology*; D012486:Salmonella typhimurium / Q000187:drug effects; D012703:Serotyping / Q000662:veterinary; D013552:Swine / Q000382:microbiology; D013553:Swine Diseases / Q000382:microbiology*