ns: not significant, ** P < 0.01, *** P < 0.001. Discussion P. fluorescens is present at low level in the human gut and has been linked to Crohn's disease (CD) [7, 8], however little is known about the potential interaction of this bacterium with the intestinal mucosa. In the present paper, we aimed at determining its potential to adhere to IEC, to induce cell cytotoxicity and trigger a proinflammatory response. We selected two strains, a classical psychrotrophic strain (MF37) and a recently characterized clinical strain

adapted to grow at 37°C (MFN1032). The behaviour of these bacteria was compared to that of the opportunistic pathogen P. aeruginosa. Since adhesion and cytotoxicity to IECs are crucial events in the infection process, the three strains were tested on two epithelial cell lines. Except for adhesion, the two IECs models Ensartinib mw used in this study gave similar responses to the three strains of Pseudomonas. Indeed, a dose dependent adhesion of bacteria to Caco-2/TC7 and HT-29 cells was observed with the greatest effect obtained with the opportunistic pathogen P. aeruginosa. It is noteworthy that, compared to the psychrotrophic strain MF37, the clinical strain

P. fluorescens MFN1032, which is adapted to develop at 37°C displayed statistically significant higher adhesion potential to HT-29 but not PXD101 concentration to Caco-2/TC7 cells. This observation suggests that the clinical strain may express a greater diversity of adhesion factors than MF37 and could explain, at least in part, the higher cytotoxicity effect of MFN1032. Although differences exist between surface proteins expressed by Caco-2/TC7 and HT-29 cell lines in comparison to normal human IECs, our results support the hypothesis that P. second fluorescens should be able to colonize the intestinal

mucosa. Pseudomonad are rarely searched for and detected as fecal bacteria, and are usually considered as a sub-dominant population [22]. In addition, there is now ample evidence that the circulating bacterial population in the intestinal lumen is very different from the resident microbiota that comes in contact with the apical surface of the enterocytes and is tightly associated to the mucus/glycocalyx layer [23, 24]. For an aerobic bacterium such as P. fluorescens, the best ecological niche should be at the vicinity of the epithelium, where oxygen concentration is the highest in the intestinal environment [25]. This is supported by the evidence showing that the P. fluorescens-specific I2 antigen sequence is systematically detected in ileal mucosa samples [7]. Moreover, in CD patients, there is a positive correlation between blood level of circulating anti-I2 antibodies and the severity of the disease [8] suggesting that the I2-producing bacteria, i.e. P. fluorescens, are in close contact with enterocytes and could contribute to CD pathogenesis. The LDH release assay showed that the cytotoxicity of P. fluorescens on Caco-2/TC7 and HT-29 cells is lower than that of P.