Factors affecting the validity of the C-13-urea breath test for in vivo determination of Helicobacter pylori infection status in a mouse model

Background. The mouse model using a human isolate of Helicobacter pylori is bring widely accepted as an economical means of studying gastric infection . A noninvasive monitoring method would be useful for repeated testing to e stablish the time course of infection and the efficacy of treatments. In th is study, we describe factors that affect interpretation of C-13 urea breat h test results for the assessment of H, pylori infection status in this mod el. Materials and Methods. Female C57Bl/6 mice that underwent gavage with H. py lori or saline were breath-tested using 50 mu g of C-13 urea at intervals u p to 2 months after inoculation. The generation of (CO2)-C-13 (excess delta (CO2)-C-13) by infected mice was compared to that of uninfected controls. The effects of diet, fasting, and coprophagy on the reliability of the C-13 urea breath test were quantitated. Results. Both commercial and synthetic mouse diets exhibited marked in vitr o urease activity. A minimum fasting time of 13 hours prior to breath testi ng significantly reduced this dietary contribution to excess delta (CO2)-C- 13 values. The coprophagic tendency of the mice caused spuriously high exce ss delta (CO2)-C-13 counts in the breath of both control and H. pylori-infe cted mice. Conclusions. Although the dietary contribution to spuriously high values of excess delta (CO2)-C-13 in mice breath-tested for H. pylori infection was reduced by fasting, the high nonspecific urease activity generated by copro phagy severely limited the reliability of the urea breath test in the asses sment of H. pylori infection status.