Mitogenic Factor(s) of Colonic Bacteria Stimulate DNA Synthesis in a Human Colonic Epithelial Cell Line

Abstract

Previous studies in vitro show that intraluminal bacteria increase DNA synthesis in the intestinal epithelium. The aim of this study was to examine in vitro whether supernatant solutions and various fractions of bacterial cells influence DNA synthesis in an epithelial cell line of human colon (LS 123). Methods: Strains of Gram-positive ( Lactobacillus acidophilus and Lactobacillus fermentum )and Gram-negative bacteria ( Escherichia coli K12 and Bacteroides thetaiotaomicron ) were selected. In addition to supernatant solutions, bacterial cell fractions containing either cell wall:membranes, cytosol, nonsoluble intracellular components or dead bacteria were separated by means of multistep centrifugation, French press, and microfiltration. DNA synthesis (labelling index) was estimated on autoradiographs of LS-123 cells. These cells had previously been labelled with tritiated thymidine following incubation with different concentrations of the supernatant solutions and fractions described above (1/2000–1/250). Results: The supernatant and all the fractions of E. coli significantly increased the labelling index in LS-123 cells (p<0.0001). Only the highest concentration of the fraction of Bacteroides thetaiotaomicron containing whole bacterial cells increased the labelling index (p<0.001). The cytosolic fraction of Lactobacillus acidophilus significantly increased DNA synthesis at the higher dose range (p<0.001). Conclusions: The microflora contains bacterial strains possessing hitherto unknown factor(s) that stimulate DNA synthesis in intestinal epithelial cells in vitro . Our results suggest that at least the cell wall of E. coli K12 and the cytosol of the Gram-positive strain Lactobacillus acidophilus are sources of epithelial cell mitogen(s). Keywords: Bacteroides thetaiotaomicron , cell division, colon, Escherichia coli , Lactobacillus acidophilus , LS-123 cells.