The effect of mucin on bacterial translocation in I-407 fetal and Caco-2 adult enterocyte cultured cell lines

Although the intestinal mucosa forms a crucial barrier between the host and the environment, bacterial translocation (BT) occurs frequently in neonates and may be a source of sepsis. The intestinal mucous gel layer is thought to be a vital component of the gut barrier and is composed, in part, of a family of glycoproteins known as mucins. Our aim was to study the effects of mucin on BT in an enterocyte cell-culture model using a fetal (I-407) and an adult (Caco-2) intestinal cell line. I-407 and Caco-2 cells were grown to confluence on porous filters in a two-chamber Transwell system. The integrity of the monolayers was confirmed by transepithelial electrical resistance (TEER) and permeability using the macromolecule dextran blue. Cells were treated with mucin (40 mg/ml) prior to inoculation of 1 x 10⁶ Escherichia coli C25. The magnitude of BT was determined quantitatively by culturing the samples from the basal chamber of the wells and was expressed as log 10 [Colony Forming Units (CFU)/ml]. Statistical analysis was performed by the Mann-Whitney U test with statistical significance at P < 0.05. Mucin inhibited BT across both fetal and adult cultured enterocyte monolayers; however, the inhibitory effect was less on the fetal cells compared to the adult cells. Dextran-blue studies showed that monolayers were intact throughout the experiments. Despite 98% inhibition of BT, mucin had a statistically significant effect on post-bacterial inoculation TEER in Caco-2 cells and no effect in I-407 cells. The ability of mucin, a mucous-barrier glycoprotein, to inhibit BT across immature intestinal enterocytes, as in the neonate, may be diminished compared to mature adult enterocytes.