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

Abstract

Background. The mouse model using a human isolate of Helicobacter pylori is being widely accepted as an economical means of studying gastric infection. A noninvasive monitoring method would be useful for repeated testing to establish the time course of infection and the efficacy of treatments. In this study, we describe factors that affect interpretation of 13C urea breath test results for the assessment of H. pylori infection status in this model. Materials and Methods. Female C57Bl/6 mice that underwent gavage with H. pylori or saline were breath-tested using 50 μg of 13C urea at intervals up to 2 months after inoculation. The generation of 13CO2 (excess δ13CO2) by infected mice was compared to that of uninfected controls. The effects of diet, fasting, and coprophagy on the reliability of the 13C urea breath test were quantitated. Results. Both commercial and synthetic mouse diets exhibited marked in vitro urease activity. A minimum fasting time of 13 hours prior to breath testing significantly reduced this dietary contribution to excess δ13CO2 values. The coprophagic tendency of the mice caused spuriously high excess δ13CO2 counts in the breath of both control and H. pylori–infected mice. Conclusions. Although the dietary contribution to spuriously high values of excess δ13CO2 in mice breath-tested for H. pylori infection was reduced by fasting, the high nonspecific urease activity generated by coprophagy severely limited the reliability of the urea breath test in the assessment of H. pylori infection status.