Enterotoxigenic Escherichia coli and Salmonella enterica Typhimurium induce mitochondrial dysfunction, inflammation and oxidative stress conditions in porcine intestinal epithelial cells

Antibiotics have been extensively used to control intestinal bacterial infections in swine production, but the actual treat associated with the emergence of antibiotic-resistant bacteria has increased the need for the development of alternative strategies. To achieve this goal, the mechanisms of infection of intestinal cells by pathogenic bacteria must be characterized. Mounting evidence indicates that mitochondria are the target of an increasing number of  bacteria. In this study, porcine intestinal epithelial IPEC J2 cells were used as a model of intestinal infection by enterotoxigenic E. coli (ETEC) and Salmonella enterica Typhimurium ( S. Typhi ). The effects of a two hours period exposure to these enteropathogens on basal mitochondrial respiration and ATP production were assessed using an Agilent Seahorse XFe Extracellular Flux Analyzer. These functional measurements indicated that both bacteria negatively affect mitochondrial energy metabolism as revealed by statistically significant decreases of basal respiration (51% and 33% of controls for ETEC and S. Typhi respectively) and ATP production (60% and 20% of controls for ETEC and S. Typhi respectively). Mitochondrial energy metabolism, oxidative stress, inflammation and apoptosis were analysed by measuring the mRNA expression of genes using specific RT 2 Profiler™ PCR Arrays (Qiagen). These analyses revealed that both bacteria increase the expression of specific genes implicated in the triggering of inflammatory, oxidative stress and apoptosis processes while only few genes implicated in mitochondrial energy metabolism were found to be modulated.  The expression of relevant genes identified in these arrays was further evaluated by quantitative RT-PCR. These analyses confirmed that the expression of genes encoding crucial inflammatory molecules (TNFα, IL1α and CCL20), major apoptosis modulators (Caspase 3 and BMP4) and oxidative stress associated proteins (DUSP1 and MCL1) were significantly affected by both bacteria. Taken together, these results shed some light on the mechanisms of infection of ETEC and Salmonella in IPEC-J2 cells.