| Summary: | Probiotics play an important role against infectious pathogens, such as <i>Escherichia coli</i> (<i>E. coli</i>), mainly through the production of antimicrobial compounds and their immunomodulatory effect. This protection can be detected both on the live probiotic microorganisms and in their inactive forms (paraprobiotics). Probiotics may affect different cells involved in immunity, such as macrophages. Macrophages are activated through contact with microorganisms or their products (lipopolysaccharides, endotoxins or cell walls). The aim of this work was the evaluation of the effect of two probiotic bacteria (<i>Escherichia coli</i> Nissle 1917 and <i>Bifidobacterium animalis</i> subsp. <i>lactis</i> HN019 on macrophage cell line J774A.1 when challenged with two pathogenic strains of <i>E. coli</i>. Macrophage activation was revealed through the detection of reactive oxygen (ROS) and nitrogen (RNS) species by flow cytometry. The effect varied depending on the kind of probiotic preparation (immunobiotic, paraprobiotic or postbiotic) and on the strain of <i>E. coli</i> (enterohemorrhagic or enteropathogenic). A clear immunomodulatory effect was observed in all cases. A higher production of ROS compared with RNS was also observed.
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