Development of a chemiluminescent urease activity assay for Helicobacter pylori infection diagnosis in gastric mucosa biopsies.

A chemiluminescent urease activity assay has been developed and optimized using the chemiluminescent pH indicator phthalhydrazidylazoacetylacetone. This compound is stable at pH </= 7 and decomposes at higher pH values, emitting light in the presence of H2O2. Urease catalyzes hydrolysis of urea to form NH3 and CO2 which increase the pH of the reaction medium, thus allowing the chemiluminescent indicator to decompose and produce photons. The emitted light is proportional to the urease activity when urea is in excess. Urease tests based on colorimetric pH indicators like phenol red are commercially available and commonly used for the rapid diagnosis of Helicobacter pylori infection in gastric mucosa biopsy specimens, since this bacterium produces high amounts of urease. Such colorimetric tests often lack sensitivity, giving false-negative results. The developed chemiluminescent test proved to be at least 50-fold more sensitive than the colorimetric tests, permitting early diagnosis of infection, and it is more rapid, giving results in 1-10 min compared to 30 min. Further applications of this assay could be the in situ localization of urease activity, corresponding to the presence of H. pylori, in gastric mucosa cryosections and the development of high-throughput screening assays of antimicrobial drugs able to inactivate the bacterium.