Aim-To establish a competitive PCR (cPCR) assay for quantitation of H pylori organisms in dental plaque samples. Methods-The cPCR coamplified target H pylori DNA and a known amount of internal standard template in the same tube with the same primers directed to 0.86 kb DNA of H pylori. The internal standard was a synthesised DNA bearing the same primer recognition sites at two ends and a non-homologous core sequence as the target DNA fragment. Quantitation was based on determination of the relative, not absolute, amounts of the diVerently sized and [ 32 P]-dCTP labelled products derived from H pylori DNA and the competitive internal standard after gel electrophoresis separation. Results-A significant correlation between known amounts of H pylori added to dental plaque samples and the results of the cPCR was found, and a standard line was developed which allowed quantitation of H pylori in the plaque samples. cPCR was performed on supragingival plaque samples from 10 adult patients with H pylori infection in the stomach, and from five adults and six children without H pylori infection in the stomach. The ranges of H pylori numbers were 1-213 (median 25), 6-76 (10), and 4-94 (14) cells/mg of dental plaque in the three groups, respectively. Conclusions-cPCR is useful for quantitation of H pylori in supragingival dental plaque samples; however, the number of the organisms in dental plaque samples seems very low. (J Clin Pathol 2000;53:218-222)

This study was designed to compare different primer sets for PCR analysis of H. pylori in the same series of 40 dental plaque samples. Three pairs of primers, HPU1/HPU2, HP1/HP2, and EHC-U/EHC-L, directed to the urease A gene, 16S rRNA gene, or 860-bp DNA of H. pylori, respectively, were used. Our results demonstrate that EHC-L/EHC-U were more specific and sensitive for H. pylori added to saliva or dental plaque than HPU1/HPU2 and HP1/HP2. The detection rates for H. pylori DNA in dental plaque samples from randomly selected adult patients from the Dental Clinic of the University of Ulm were 26.5% (9/34) for HPU1/HPU2, 78.9% (30/38) for HP1/HP2, and 100% (40/40) for EHC-U/EHC-L (P < 0.001). Nested PCR using primers directed to the 860-bp DNA of H. pylori further confirmed the presence of H. pylori DNA (40/40) in all these samples. Our results indicate that primers EHC-U/EHC-L are to be recommended for PCR detection of H. pylori in the oral cavity.