Localization of Tropheryma whippelii rRNA in tissues from patients with Whipple's disease

Whipple's disease is caused by a cultivation-resistant bacterium, Tropheryma whippelii. Ultrastructural studies of intestinal biopsy specimens from patients with Whipple's disease have shown that intracellular and extracellular bacteria are present, but the preferred site of growth is unknown. Tissue sections from 8 patients with Whipple's disease and from 19 healthy control subjects were analyzed by use of fluorescence in situ hybridization and laser scanning confocal microscopy, to determine the location of rRNA that would indicate the presence of metabolically active bacteria. T. whippelii rRNA was most prevalent near the tips of intestinal villi, in the lamina propria, just basal to epithelial cells. Most of the bacterial rRNA signal appeared to be located between cells and did not colocalize with the human intracellular protein vimentin. The location of bacterial rRNA in tissues from patients with Whipple's disease provides evidence that bacteria are growing outside cells and suggests that T. whippelii is not an obligate intracellular pathogen.