Abstract
Cultures of Helicobacter pylori obtained from the American Type Culture Collection (strain 43504) were grown as isolated colonies or lawns on blood agar plates and in broth culture with constant shaking. Examination of bacterial growth with Gram-stained fixed preparation and differential interference contrast microscopy on wet preparations revealed that bacteria grown on blood agar plates had a morphology consistent with that normally reported for H. pylori whereas bacteria from broth cultures had the morphologic appearance of Helicobacter heilmannii. Bacteria harvested from blood agar plates assumed an H. heilmannii-like morphology when transferred to broth cultures, and bacteria from broth cultures grew with morphology typical of H. pylori when grown on blood agar plates. Analysis by PCR of bacteria isolated from blood agar plates and broth cultures indicated that a single strain of bacteria (H. pylori) was responsible for both morphologies.