Background: Because of in vivo limitations, the mechanisms underlying the process of bacterial translocation are poorly understood. Thus, an in vitro model system to study the translocation process was developed.
Methods: Transformed human colonic carcinoma (Caco-2) intestinal cells were grown as a polarized monolayer on semi-permeable membranes contained in the upper compartment of a two-compartment system. Once the Caco-2 monolayer had reached confluence, the ability of six different species of bacteria to translocate across the monolayer was tested using a dose-response curve of bacteria (10(2), 10(4), or 10(6)) organisms.
Results: At inocula of 10(4) or 10(6) but not 10(2) organisms, bacteria crossed the monolayer. Bacterial passage across the monolayer was bacterial species specific, with gram-negative enterics being the best, gram-positive aerobes being intermediate translocators, and strict anaerobes being the poorest translocators.
Conclusion: The results of this study indicate that bacteria translocate across the Caco-2 monolayer in a dose-dependent and species-related fashion and support the use of this in vitro epithelial cell culture system as a model for studying bacterial transport.