RESUMO
AIM: To develop a reliable method for measuring urease activity in live bacteria, and to determine whether there are any differences in urease activity among the Helicobacter pylori strains involved in gastroduodenal disease. DESIGN: The stability of the method was examined in the first phase of the study, and in a second phase the mean urease activity in clinical isolates from different groups of patients was compared. MATERIALS AND METHODS: To assess the stability and reliability of the method, we assessed the relationship between bacterial proliferation and urease activity, the relationship between the number of bacteria and the optical density, and differences in urease activity among bacterial generations. Ten of the 3-day-old colonies in the third generation were suspended in phosphate-buffered saline, and urease activity was measured as 10(5) colony-forming units/ml bacteria. RESULTS: The assay system appeared to be effective, because the urease activity of live bacteria in the logarithmic growth period was constant, the number of bacteria and the optical density showed a linear correlation on a bilogarithmic graph and there was no significant difference in urease activity over three generations. With this method, urease activity varied from 0.192 to 80.42 mIU/10(5) colony-forming units of bacteria/ml. There was no significant difference in the mean urease activity of live bacteria from controls, gastric ulcer patients and duodenal ulcer patients. However, the mean urease activity in bacteria from cancer patients was significantly higher than that of controls or duodenal ulcer patients. CONCLUSIONS: H. pylori strains derived from cancer patients, which have relatively high levels of urease activity, might easily colonize the stomach and lead to much mucosal damage during the long course of H. pylori infection.
