Abstract
Pseudomonas aeruginosa can penetrate the layer of mucus formed by host intestinal epithelial cells, often resulting in sepsis in immunocompromised patients. We have previously demonstrated that P. aeruginosa can penetrate the mucin layer by flagellar motility and the degradation of the mucin layer. However, it remains unclear how P. aeruginosa initially recognizes epithelial cells. Using the human epithelial colorectal adenocarcinoma (Caco-2) cell line, we investigated extracellular signaling that could facilitate the penetration of P. aeruginosa through the mucin layer. The supernatant from Caco-2 cell cultures increased penetration of P. aeruginosa through an artificial mucin layer. The Caco-2 cell supernatant increased bacterial flagella-dependent swarming motility, but it did not influence P. aeruginosa growth or protease activity. Filtering of the Caco-2 cell supernatant indicated that proteins weighing <10 kDa increased mucin penetration, swarming motility, and, based on a tethered cell assay, induced acceleration of the flagellar filament rotational rate. Furthermore, a capillary assay showed that <10 kDa proteins in the Caco-2 cell supernatant attracted P. aeruginosa cells. Finally, we identified that growth-regulated oncogene-α (GRO-α) secreted by Caco-2 cells was a factor facilitating flagellar filament rotation and swarming motility, although it did not attract the bacteria. We conclude that penetration of the mucin layer by P. aeruginosa is facilitated by small proteins (<10 kDa) secreted by Caco-2 cells, both by inducing acceleration of flagellar motility and increasing chemotaxis.
Highlights
The translocation of pathogens from the gut into the blood requires them to cross at least two barriers: the mucus layer and the tight junctions formed by epithelial cells (Dharmani et al, 2009; Tlaskalova-Hogenova et al, 2011)
To clarify the mechanism by which P. aeruginosa recognizes extracellular signals of the intestinal epithelial cells using the human intestinal epithelial Caco-2 cell line (Okuda et al, 2010; Hayashi et al, 2013, 2015; Shikata et al, 2016), we examined the effects of Caco-2 cell culture supernatants on mucin penetration by the P. aeruginosa PAO1 strain
We examined the effects of the supernatant of Caco2 cells cultured in vitro on mucin penetration by the P. aeruginosa PAO1 strain to clarify the mechanism by which P. aeruginosa recognizes extracellular signals from intestinal epithelial cells to facilitate bacterial translocation
Summary
The translocation of pathogens from the gut into the blood requires them to cross at least two barriers: the mucus layer and the tight junctions formed by epithelial cells (Dharmani et al, 2009; Tlaskalova-Hogenova et al, 2011). Host defenses include complex mechanisms of the innate immune system, such as phagocytosis by macrophages, dendritic cells, and neutrophils. These cells are attracted to the infection site by chemokines and play an important role in removing pathogens (Janeway and Medzhitov, 2002; Gellatly and Hancock, 2013; Sallenave, 2014). Better understanding of opportunistic P. aeruginosa infections requires clarification of the mechanisms by which it penetrates the protective barriers and escapes the immune system defenses
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