Comparison of the biochemical changes in the jejunal mucosa of dogs with aerobic and anaerobic bacterial overgrowth

Subcellular biochemical changes in the jejunal mucosa have been compared in dogs with either aerobic or anaerobic bacterial overgrowth to explore relationships between composition of the flora and mucosal damage. Affected animals comprised 17 German shepherd dogs with chronic diarrhea or weight loss, or both. Analysis of duodenal juice demonstrated aerobic overgrowth in 10 cases, most frequently comprising enterococci and Escherichia coli, and obligate anaerobic overgrowth in 7 cases, most frequently including Clostridia spp. Histologic changes were minimal; however, examination of peroral jejunal biopsy specimens by sucrose density gradient centrifugation revealed specific biochemical abnormalities. In the dogs with aerobic overgrowth, there was a selective loss of brush border alkaline phosphatase activity, and gamma-glutamyl transferase activity was increased, whereas activities of disaccharidases and aminopeptidase N were unaltered. In contrast, anaerobic overgrowth was associated with a reduction in brush border density, indicative of a considerable fall in the glycoprotein-to-lipid ratio of the brush border membrane, whereas brush border enzyme activities were unaltered. There was a loss of peroxisomal catalase activity in dogs with aerobic overgrowth, and an indication of mitochondrial disruption in dogs with anaerobic overgrowth, but little evidence for damage to other subcellular organelles. These findings demonstrate that aerobic and anaerobic overgrowth may be associated with distinct but different mucosal abnormalities particularly affecting the brush border membrane.