In vitro and in vivo effects of the probiotic Escherichia coli strain M-17:: immunomodulation and attenuation of murine colitis

We examined the in vitro and in vivo effects of a probiotic, Escherichia coli strain M-17 (EC-M17), on NF-kappa B signalling, cytokine secretion and efficacy in dextran sulfate sodium (DSS)-induced murine colitis. NF-kappa B signalling was assessed using an NF-kappa B luciferase reporter cell line that was stimulated with TNF-alpha (100 ng/ml). p65 Nuclear binding and cytokine secretion (TNF-alpha, IL-1 beta and IL-6) were evaluated using a RAW 264.7 macrophage cell line that was exposed to lipopolysaccharide (LPS; 5 mu g/ml). Mice were administered vehicle, EC-M17, metronidazole, or EC-M17 plus metronidazole for 13 d. During the final 6 d, mice also received 2% DSS. Parameters evaluated included disease activity index (DAI), histology, myeloperoxidase and NF-kappa B p65. EC-M17 dose dependently inhibited TNF-alpha-induced NF-kappa B signalling. At 5 X 109 colony-forming units/ml, EC-M17 inhibited NF-kappa B by > 95%. LPS-induced nuclear p65 binding was significantly inhibited (78%; P < 0.05) in RAW 264.7 macrophages at 1 x 10(8) colony-forming units/ml. EC-M17 also inhibited (by > 90%) the LPS-induced secretion of TNF-alpha, IL-1 beta and IL-6. In mice with DSS-induced colitis, EC-M17, metronidazole, and EC-M17 plus metronidazole significantly reduced DAI and colonic histology scores. Both EC-M17 and metronidazole reduced colonic IL-12, IL-6, IL-1 beta and interferon-gamma. The combination of EC-M17 plus metronidazole resulted in more substantial cytokine reductions than were found with either treatment alone, and combination therapy significantly (P < 0.05 in both cases) reduced IL-1 beta compared with EC-M17 and colonic histology scores compared with metronidazole. Alone, and in combination with metronidazole, EC-M17 improved murine colitis, probably due to an inhibitory effect on NF-kappa B signalling.