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Pretreatment with the probiotic Escherichia colistrain Nissle 1917 (EcN) was assessed in a pig model of intestinal infection to prevent acute secretory diarrhea. In the model 10(10) colony forming units of the porcine enterotoxigenic Escherichia coli Abbotstown (EcA) was given via orogastric tube to weaned piglets at day 21 postpartum (-EcN/+EcA group, n = 7). Forty-eight hours after challenge electrophysiological parameters of isolated intact jejunal epithelia were characterized in Ussing chambers. In agreement with clinical signs of diarrhea, tissues of challenged animals showed an overshoot of secretory response after stimulation of the cAMP-mediated second messenger pathway by forskolin, indicating higher excitability of chloride secretory systems under infected conditions. The data were compared with respective measurements from animals that got a daily dose of 10(10) cfu of the probiotic EcN over 10 days before EcA challenge (+EcN/+EcA group; n = 4), from a group that received only EcN (+EcN/-EcA; n = 4), or from a group that remained totally untreated (-EcN/-EcA; n = 6). EcN pretreatment completely abolished clinical signs of secretory diarrhea in +EcN/+EcA animals. Furthermore, jejunum epithelia of these animals did not exhibit an overshoot of secretory response upon stimulation with forskolin. Our studies demonstrate for the first time the efficacy of prophylactic EcN in pig small intestine for preventing an effect of toxigenic EcA. This infection model with freshly weaned piglets may be predestinated to further characterize EcN effects on the cellular level, i.e., involved second messenger pathways, or it may also be useful to examine the efficacy of other substrates or microbe strains against secretory stimuli.