Secretion analysis of invading process between Salmonella typhimurium and HT-29 intestinal epithelial cells on the microfluidic chip

In this study, a contact co-culture model of bacteria and cells on a microfluidic chip with arrayed circular chambers was established to simulate the invasion process of Salmonella typhimurium (S. typhimurium) into HT-29 intestinal epithelial cells. The interaction process was observed and detected in situ on the designed microchip. By optimizing the structure and size of the chambers and microchannels, the microchip was found to be more suitable for microscopic in situ observation. Cell viability, morphology, cytoskeleton and secretions during the invasion process of S. typhimurium into HT-29 intestinal epithelial cells were detected. In the experiments, the cells formed multicellular aggregates, and the cell cytoskeleton rearranged to undergo pinocytosis after exposure to S. typhimurium. Cell viability was shown to continuously decrease during the process. Furthermore, cell viability was found to positively correlate with cytoskeleton damage, and cell cytoskeleton regulated the cell morphology. The cell secretion level of the pro-inflammatory cytokine IL-8 in the co-culture supernatants was measured using enzyme-linked immunosorbent assay (ELISA). It was observed that the level of IL-8 increased rapidly when S. typhimurium invaded HT-29 intestinal epithelial cells, reached a peak of 4.45 pg mL-1 at 3 h, and then continuously dropped until it reached the baseline level of 1.04 pg mL-1 at 12 h. The designed microfluidic chip could provide a unique way to study the interaction between a pathogen and the invaded cells and guide the analysis of bacterial infection and other related research.