Enhancement of immunohistochemical detection of Salmonella in tissues of experimentally infected pigs

Abstract

<p><em>Salmonella</em> Typhimurium is one of the main pathogens compromising porcine and human health as well as food safety, because it is a prevailing source of foodborne infections due to contaminated pork. A prominent problem in the management of this bacteriosis is the number of subclinically infected carrier pigs. As very little is known concerning the mechanisms allowing <em>Salmonella</em> to persist in pigs, the objective of this study was to develop an immunohistochemical approach for the detection of salmonellae in tissue of pigs experimentally infected with <em>Salmonella</em> Typhimurium. Samples were obtained from a challenge trial in which piglets of the German Landrace were intragastrically infected with <em>Salmonella</em> enterica serovar Typhimurium DT104 (1.4-2.1x10¹⁰ CFU). Piglets were sacrificed on days 2 and 28 post infection. Tissue samples of jejunum, ileum, colon, ileocecal mesenteric lymph nodes (<em>Lnn. ileocolici</em>), and tonsils (<em>Tonsilla veli palatini</em>) were fixed in Zamboni’s fixative and paraffin-embedded. Different immunohistochemical staining protocols were evaluated. <em>Salmonella</em> was detected in varying amounts in the tissues. Brown iron-containing pigments in the lymph nodes interfered with the identification of <em>Salmonella</em> if DAB was used as a staining reagent. Detergents like Triton X-100 or Saponin enhanced the sensitivity. It seems advisable not to use a detection system with brown staining for bacteria in an experimental setup involving intestinal damage including haemorrhage. The use of detergents appears to result in a higher sensitivity in the immunohistochemical detection of salmonellae.</p>