Abstract
BackgroundPseudomonas fluorescens is present in low number in the intestinal lumen and has been proposed to play a role in Crohn's disease (CD). Indeed, a highly specific antigen, I2, has been detected in CD patients and correlated to the severity of the disease. We aimed to determine whether P. fluorescens was able to adhere to human intestinal epithelial cells (IECs), induce cytotoxicity and activate a proinflammatory response.ResultsBehaviour of the clinical strain P. fluorescens MFN1032 was compared to that of the psychrotrophic strain P. fluorescens MF37 and the opportunistic pathogen P. aeruginosa PAO1. Both strains of P. fluorescens were found to adhere on Caco-2/TC7 and HT-29 cells. Their cytotoxicity towards these two cell lines determined by LDH release assays was dose-dependent and higher for the clinical strain MFN1032 than for MF37 but lower than P. aeruginosa PAO1. The two strains of P. fluorescens also induced IL-8 secretion by Caco-2/TC7 and HT-29 cells via the AP-1 signaling pathway whereas P. aeruginosa PAO1 potentially used the NF-κB pathway.ConclusionsThe present work shows, for the first time, that P. fluorescens MFN1032 is able to adhere to IECs, exert cytotoxic effects and induce a proinflammatory reaction. Our results are consistent with a possible contribution of P. fluorescens in CD and could explain the presence of specific antibodies against this bacterium in the blood of patients.
Highlights
Pseudomonas fluorescens is present in low number in the intestinal lumen and has been proposed to play a role in Crohn’s disease (CD)
Adhesion to intestinal epithelial cells The binding index of the clinical strain P. fluorescens MFN1032 on Caco-2/TC7 and HT-29 cells was determined after 5 h of incubation and compared to P. fluorescens MF37 and P. aeruginosa PAO1
When the cells were infected with a 106 CFU or 108 CFU ml-1 bacterial solution, the mean adhesion index of P. aeruginosa PAO1 reached 12.6 ± 2.6 or 32.1 ± 1.9 bacteria cell-1, respectively, whereas the adhesion of P. fluorescens was quite similar for the two strains with 10.6 ± 0.5 or
Summary
Pseudomonas fluorescens is present in low number in the intestinal lumen and has been proposed to play a role in Crohn’s disease (CD). We aimed to determine whether P. fluorescens was able to adhere to human intestinal epithelial cells (IECs), induce cytotoxicity and activate a proinflammatory response. Human IECs infected with pathogenic bacteria generally produce proinflammatory cytokines, such as interleukin (IL)-8 [9] The latter has a chemotactic role and can recruit polymorphonuclear cells into the infected site and promote their infiltration of the epithelial layer infected by invasive or noninvasive bacteria [10,11]. Epithelial NF-B preserves the integrity of the gut epithelial barrier and coordinates the antimicrobial actions of the innate and adaptive immune systems [15] Hyperactivation of this transcription factor results in chronic inflammatory bowel diseases [16]. Activation of AP-1 is dependent on mitogen-activated protein kinases (MAPK) that are central in many physiological processes, including regulation of cytokine and stress responses and cytoskeletal reorganization [17,18]
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