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Early Epithelial Invasion by Salmonella enterica Serovar Typhimurium DT104 in the Swine Ileum

Departments of Veterinary Microbiology (DKM) and Veterinary Pathology (MRA), Iowa State University, Ames, IA; PreHarvest Food Safety and Enteric Disease Unit, National Animal Disease Center, Agricultural Research Service, United States Department of Agriculture, Ames, IA (TJS, SAC); Department of Microbiology, University of Iowa, Iowa City, IA (BDJ); and Institut fur Pathologie, Tierärzliche Hochschule Hannover, Hannover, Germany (JP)

Salmonella enterica serovar Typhimurium is an important intestinal pathogen in swine. This study was performed to document the early cellular invasion of Salmonella serovar Typhimurium in swine ileum. Ileal gut-loops were surgically prepared in ten 4- to 5-week-old mixed-breed pigs and inoculated for 0–60 minutes. Loops were harvested and prepared for both scanning and transmission electron microscopy (SEM and TEM, respectively). Preferential bacterial adherence to microfold cells (M cells) was seen within 5 minutes, and by 10 minutes bacterial invasion of the apical membrane was seen in M cells, goblet cells, and enterocytes. This multicellular invasion was observed throughout the course of infection. In addition, SEM revealed a specific affinity of Salmonella serovar Typhimurium to sites of cell extrusion. Using TEM, bacteria in these areas were focused in the crevices formed by the extruding cell and the adjacent cells and in the cytoplasm immediately beneath the extruding cell. Our results suggest that early cellular invasion by Salmonella serovar Typhimurium is nonspecific and rapid in swine. Furthermore, the combination of SEM and TEM data suggests that Salmonella serovar Typhimurium may use sites of cell extrusion as an additional mechanism for early invasion.

Key words: DT104; electron microscopy; enterocyte; extrusion; ileum; invasion; Salmonella; swine; Typhimurium.

Requests reprints from Dr. T. J. Stabel, National Animal Disease Center, 2300 Dayton Avenue, Ames, IA 50010 (USA). E-mail: tstabel{at}nadc.ars.usda.gov.

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