PCR detection of clarithromycin-susceptible and -resistant Helicobacter pylori from formalin-fixed, paraffin-embedded gastric biopsies.

Antimicrobial resistance to clarithromycin is a growing concern in the treatment of Helicobacter pylori and is associated with three major point mutations of the 23S rRNA, A2142C, A2142G, and A2143G. The use of traditional culture-based methods for determination of clarithromycin resistance in H. pylori are time consuming and lack sensitivity. We implemented a real-time PCR with melt curve analysis to detect and characterize H. pylori in formalin-fixed, paraffin-embedded gastric biopsy specimens to assess the frequency of clarithromycin resistance mutations in our study population. One hundred and fifty-three formalin-fixed, paraffin-embedded gastric biopsies were chosen on the basis of positive immunohistochemical staining for H. pylori and an accompanying histopathological diagnosis of Helicobacter-associated gastritis. New adjacent sections were taken for immunohistochemical staining and DNA extraction with subsequent testing by PCR assay and melt curve analysis using a primer and probe combination first described by Oleastro et al.(12) One hundred and forty-six samples demonstrated adequate amplification of a human DNA control target. Of these, there were 122 H. pylori immunohistochemistry-positive samples. In all, 103 out of 122 (84%) immunohistochemistry-positive samples demonstrated amplifiable H. pylori 23S rRNA gene target and 19 (16%) demonstrated no amplification of H. pylori. Twenty-two samples were negative for H. pylori by immunohistochemistry and PCR. Two were negative for H. pylori by immunohistochemistry, but were positive for H. pylori by PCR. In all, 52 out of 105 (50%) PCR-positive samples demonstrated resistance mutations, and it was determined that a heterogeneous population of mutated and unmutated organisms was present in 11 out of 52 samples. The use of PCR assays allows for a timely assessment of clarithromycin resistance status without the disadvantages of culture-based methods, and may lead to a decrease in treatment failure rates.