Enhancement of immunohisto-chemical detection of Salmonella in tissues of experimentally infected pigs

Salmonella Typhimurium is one of the main pathogens compromising porcine and human health as well as food safety, because it is a pre-vailing 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 Salmonella to persist in pigs, the objective of this study was to develop an immunohistochem-ical approach for the detection of salmonellae in tissue of pigs experimentally infected with Salmonella Typhimurium. Samples were obtained from a challenge trial in which piglets of the German Landrace were intragastrically infected with Salmonella enterica serovar Typhimurium DT104 (1.4-2.1×1010 CFU). Piglets were sacrificed on days 2 and 28 post infection. Tissue samples of jejunum, ileum, colon, ileoce-cal mesenteric lymph nodes (Lnn. ileocolici), and tonsils (Tonsilla veli palatini) were fixed in Zamboni’s fixative and paraffin-embedded. Different immunohistochemical staining proto-cols were evaluated. Salmonella was detected in varying amounts in the tissues. Brown iron-con-taining pigments in the lymph nodes interfered with the identification of Salmonella if DAB was used as a staining reagent. Detergents like Triton X-100 or Saponin enhanced the sensitivi-ty. It seems advisable not to use a detection sys-tem 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