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Aims: To test whether a hypoacidic environment may potentially "stress" Helicobacter pylori DNA, encouraging the emergence of strain variation. Methods: This hypothesis was tested by inducing prolonged hypoacidity with omeprazole, a potent antisecretory drug. The genomic DNA ofHpylori was studied by electrophoretic separation of restriction endonuclease fragments followed by rRNA gene hybridisation in seven patients infected with H pylori before and after treatment with omeprazole 20-40 mg daily for six to eight weeks. DNA was isolated and purified using the guanidium thiocyanate reagent method. DNA samples were digested with Hae III, electrophoresed, vacublotted, and hybridised using a biotinylated cDNA probe prepared from 16S and 23S rRNA from HpyloriNCTC 11638. Isolates were compared using their ribopatterns (DNA fingerprints). Results: A total of 26 isolates were obtained; all DNA isolates were cut by Hae III, which was the enzyme that gave the best resolved hybridisation patterns for analysis. No two patients harboured the same strain. The isolates from two patients showed evidence ofsubtypic variation; one patient had two distinct strains and four patients had their own indistinguishable strains before and after treatment with omeprazole. For each patient, the paired ribopatterns of H pylori DNA were not affected by treatment with omeprazole for six to eight weeks. Conclusion: The H pylori genome is relatively stable when exposed to the conditions of prolonged hypoacidity that result from treatment with omeprazole. Royal Free Hospital School of Medicine, London A G Fraser R E Pounder National Collection of Type Cultures, Central Public Health Laboratory, London J Bickley R J Owen Correspondence to: Professor RE Pounder MA MD FRCP, University Department of Medicine, Royal Free Hospital School of Medicine, Rowland Hill Street, London NW3 2PF, UK Accepted for publication 30 October 1991 (j Clin Pathol 1992;45:1062-1065) Helicobacter pylori is a microaerophilic bacterium frequently found in the gastric antrum of both asymptomatic subjects and those with peptic ulcer disease. ' 2 Recent work has shown that "5S-methionine-labelled protein sodium dodecyl sulphate-polyacrylamide acrylamide gel electrophoresis (SDS-PAGE), immunoblot and DNA fingerprinting based on DNA digest patterns can all be used to indentify H pylori.' However, ribopatterns provide a simpler, reproducible and sensitive method of discriminating between isolates of H pylori.4 7 A high level of genomic heterogeneity has been shown among Hpylori isolated from different patients in the United Kingdom, the Netherlands, Australia and Canada.4 "This genomic heterogeneity is more pronounced in H pylori than in many other organisms that have been studied,'2-'" hence the technique of DNA fingerprinting has clear applications for epidemiological research. The reason for the genetic heterogeneity in H pylori isolates is unclear. Although H pylori DNA fingerprints are highly stable in the laboratory, H pylori may exhibit genetic instability in vivo. Acute infection seems to be associated with a transient achlorhydria: the evidence comes from self ingestion studies'5 and from retrospective analysis of epidemics of achlorhydria in experimental laboratories which may have been due to transmission ofH pylori by contaminated nasogastric tubes.'6 19 In contrast, the acid secretion of asymptomatic volunteers found to be positive for H pylori on screening (who are likely to have been infected for several years) is normal.20 The mechanism of this transient achlorhydria is unknown, certain strains of H pylori can cause profound suppression of acid secretion in isolated human gastric glands.2' Achlorhydria causes a luminal bacterial overgrowth which may facilitate the formation of N-nitrosamine compounds22 which may damage the DNA of the original infecting H pylori. This hypothesis was tested in this study by inducing acid suppression with omeprazole. Omeprazole 30 mg daily decreases mean 24 hour intragastric acidity by 97%,23 an effect that is present both day and night. Omeprazole has been very effective in the treatment of duodenal ulceration and ulcerative oesophagitis that is resistant to standard doses of 24 H2-receptor antagonists, an effect directly related to its profound acid suppression.25 Omeprazole has been shown to increase the N-nitrosamine concentration of the gastric juice after two weeks treatment in healthy volunteers.26 Patients treated with this drug may therefore be a valid model in which to test the hypothesis. Methods Patients presenting for endoscopic investigation of their dyspepsia were identified as being infected with H pylori and requiring omeprazole treatment, because of either failure to respond to treatment with H2-receptor antagonists or because of aggressive duodenal ulceration or reflux oesophagitis. Patients taking 1062 group.bmj.com on June 19, 2017 Published by http://jcp.bmj.com/ Downloaded from