Monocolonization with Bacteroides ovatus Protects Immunodeficient SCID Mice from Mortality in Chronic Intestinal Inflammation Caused by Long-Lasting Dextran Sodium Sulfate Treatment

This study was aimed to evaluate the role of commensal Gramnegative bacterium Bacteroides ovatus in murine model of chronic intestinal inflammation. The attempt to induce chronic colitis was done in Bacteroides ovatus-monoassociated, germfree and conventional mice either in immunocompetent (BALB/c) mice or in mice with severe combined immunodeficiency (SCID), using 2.5 % dextran-sodium sulfate (DSS) in drinking water (7 days DSS, 7 days water, 7 days DSS). Conventional mice developed chronic colitis. Some of germ-free BALB/c and the majority of germ-free SCID mice did not survive the long-term treatment with DSS due to massive bleeding into the intestinal lumen. However, monocolonization of germ-free mice of both strains with Bacteroides ovatus prior to long-term treatment with DSS protected mice from bleeding, development of intestinal inflammation and precocious death. We observed that though DSS-treated Bacteroides ovatus-colonized SCID mice showed minor morphological changes in colon tissue, jejunal brushborder enzyme activities such as Y-glutamyltranspeptidase, lactase and alkaline phosphatase were significantly reduced in comparison with DSS-untreated Bacteroides ovatus-colonized mice. This modulation of the enterocyte Y-glutamyltranspeptidase localized to the brush border membrane has been described for the first time. This enzyme is known to reflect an imbalance between pro-oxidant and anti-oxidant mechanisms, which could be involved in protective effects of colonization of germ-free mice with Bacteroides ovatus against DSS injury.