RAPID COLORIMETRIC HYBRIDIZATION ASSAY FOR DETECTING AMPLIFIED HELICOBACTER-PYLORI DNA IN GASTRIC BIOPSY SPECIMENS

A very simple, practical, sensitive, and specific colorimetric hybridi zation assay for detecting amplified Helicobacter pylori DNA is descri bed. This assay, which combines a sensitive sandwich DNA hybridization reaction and a colorimetric protocol similar to those used in convent ional enzyme immunoassays, was shown to be suitable for detecting H. p ylori-infected gastric biopsy specimens and for monitoring the eradica tion of the pathogen after treatment. The specificity and sensitivity of the colorimetric hybridization assay were tested by assaying 27 H. pylori strains (4 reference and 23 clinical isolates), 9 strains of ot her Helicobacter spp. or Campylobacter spp., and 11 clinical isolates of other urease-positive bacteria. The likelihood of H. pylori detecti on in gastric biopsy specimens by the colorimetric hybridization assay was evaluated with 23 H. pylori-positive and 41 H. pylori-negative bi opsy specimens on the basis of positive and negative results, respecti vely, of culture, rapid urease test, histological examination, and PCR . Biopsy specimens from 33 treated patients, endoscopied 4 to 8 weeks after the end of treatment, were also tested. All H. pylori strains sh owed positive results in the colorimetric hybridization assay, present ing optical densities at 450 nm (OD(450)s) of greater than or equal to 3.0. None of the other Helicobacter spp., Campylobacter spp., or the clinical isolates of other urease-positive bacteria showed OD(450)s eq ual to or greater than the cutoff (mean OD450 cutoff, 0.208). The colo rimetric hybridization assay detected all 23 H. pylori-positive biopsy specimens (mean OD450 2.910 +/- 0.295), while none of the H. pylori-n egative biopsy specimens was shown to be positive in the assay (mean O D450, 0.108 +/- 0.025). H. pylori was considered to not eradicated fro m three of the posttreatment biopsy specimens by culture, rapid urease test, histological examination, and PCR. They were all positive by th e colorimetric hybridization assay, and their OD(450)s were greater th an or equal to 3.0. The colorimetric hybridization assay also detected two other H. pylori positive patients. Specimens from these two patie nts had negative culture, rapid urease test, and histology results, an d a specimen from one of them also tested negative by PCR. These resul ts indicate that the colorimetric hybridization assay is a suitable me thod both for the diagnosis of H. pylori in biopsy specimens and for t he follow-up of patients after the end of treatment.