Salmonella Typhimurium resides largely as an extracellular pathogen in porcine tonsils, independently of biofilm-associated genes csgA, csgD and adrA

Alexander van Parys , Filip Boyen , Jiri Volf , Elin Verbrugghe , Bregje Leyman , Ivan Rychlik , Freddy Haesebrouck , Frank Pasmans

Persistent Typhimurium infections in pigs are a major concern for food safety and human health. Tonsils play a key role in the persistence of Typhimurium in pigs. Previous studies indicated that virulence genes involved in invasion and intracellular survival are of little importance for the colonization of porcine tonsils, suggesting a predominantly extracellular location of the bacteria. Biofilm formation might promote extracellular persistence of Typhimurium. The aim of this study was to determine whether the bacterium resides predominantly intra- or extracellularly in tonsils of pigs and to examine the contribution of biofilm-associated genes , and in persistence in porcine tonsils. Single cell suspensions were prepared from tonsils of orally inoculated pigs (2 x 10 colony forming units (CFU) wild type Typhimurium) to determine the ratio of extracellular versus intracellular bacteria. Both at 5 and 28 days post inoculation (pi), the majority of bacteria was found extracellularly in porcine tonsils. To determine the contribution of biofilm formation in extracellular persistence, pigs were orally inoculated with a mixture of 2 x 10 CFU of the Typhimurium wild type strain and 2 x 10 CFU of one of the Typhimurium , or mutants. At ten days pi, equal numbers of both wild type and mutant bacteria were found not only in tonsils, but also in ileum, ileum contents, ileocecal lymph nodes and faeces.In conclusion, we showed that Typhimurium resides extracellularly in porcine tonsils, using a biofilm independent mechanism.

Mots clés: Typhimurium; Pig; Extracellular; Biofilm; Tonsil

Alexander van Parys, Filip Boyen, Jiri Volf, Elin Verbrugghe, Bregje Leyman, et al.. Salmonella Typhimurium resides largely as an extracellular pathogen in porcine tonsils, independently of biofilm-associated genes csgA, csgD and adrA. Veterinary Microbiology, 2009, 144 (1-2), pp.93. ⟨10.1016/j.vetmic.2009.12.021⟩. ⟨hal-00514613⟩