Immunomagnetic separation and PCR for detection of Helicobacter pylori in water and stool specimens

The detection of Helicobacter pylori in clinical and environmental samples by PCR sometimes requires removal of polymerase inhibitors. We have used a magnetic immunoseparation technique as pre-PCR treatment to facilitate direct detection of H. pylori in stool and water specimens. Rabbit hyperimmune antiserum was produced and magnetic beads were coated with purified immunoglobulin G, which reacted with and bound to both coccoid and rod-shaped forms of H. pylori. When PCR was applied for the detection of H. pylori from cultured samples, the number of organisms that was required for positive scores varied significantly. For a 3-day culture of H. pylori, samples containing 10(2) bacteria per ml are needed for a positive score; for a 6-day culture, samples containing 10(4) bacteria per ml are needed; and for a 10-day culture, samples containing 10(6) bacteria per ml are needed. These results indicate that the coccoid forms of H. pylori may have a different antigenicity and DNA content and are therefore more difficult to detect by immunomagnetic separation and PCR than the rod-shaped forms. Spiked samples with the addition of feces, spiked water samples, and a patient stool specimen were all scored positive with this technique.