HELICOBACTER-PYLORI CONTAINING ONLY CYTOPLASMIC UREASE IS SUSCEPTIBLETO ACID

Helicobacter pylori, an important etiologic agent in a variety of gast roduodenal diseases, produces large amounts of urease as an essential colonization factor. We have demonstrated previously that urease is lo cated within the cytoplasm and on the surface of H. pylori both in viv o and in stationary-phase culture. The purpose of the present study wa s to assess the relative contributions of cytoplasmic and surface-loca lized urease to the ability of H. pylori to survive exposure to acid i n the presence of urea. Toward this end, we compared the acid resistan ce in vitro of H. pylori cells which possessed only cytoplasmic urease to that of bacteria which possessed both cytoplasmic and surface-loca lized or extracellular urease. Bacteria with only cytoplasmic urease a ctivity were generated by using freshly subcultured bacteria or by tre ating repeatedly subcultured H. pylori with flurofamide (1 mu M), a po tent, but poorly diffusible urease inhibitor. H. pylori with cytoplasm ic and surface-located urease activity survived in an acid environment when 5 mM urea was present. In contrast, H. pylori with only cytoplas mic urease shows significantly reduced survival when exposed to acid i n the presence of 5 mM urea. Similarly, Escherichia coli SE5000 expres sing Ei. pylori urease and the Ni2+ transport protein NixA, which expr esses cytoplasmic urease activity at levels similar to those in wild-t ype H. pylori, survived minimally when exposed to acid in the presence of 5 to 50 mM urea. We conclude that cytoplasmic urease activity alon e is not sufficient (although cytoplasmic urease activity is likely to be necessary) to allow survival of H. pylori in acid; the activity of surface-localized urease is essential for resistance of H. pylori to acid under the assay conditions used. Therefore, the mechanism whereby urease becomes associated with the surface of H. pylori, which involv es release of the enzyme from bacteria due to autolysis followed by ad sorption of the enzyme to the surface of intact bacteria (''altruistic autolysis''), is essential for survival of H. pylori in an acid envir onment. The ability of H. pylori to survive exposure to low pH is like ly to depend on a combination of both cytoplasmic and surface-associat ed urease activities.