Effect of culture conditions on morphological changes of Helicobacter pylori

The morphological conversion of Helicobacter pylori from the spiral form to the coccoid form may be the expression of a transitory adaptation to an un suitable environment. The mechanism(s) of this conversion are not clear. In this study, we examined whether the morphological conversion of H. pylori is affected by various culture conditions, such as oxygen concentration, pH , temperature, or the presence of beta-cyclodextrin. H. pylori (NTCC11916) was cultured on Brucella agar, followed by culture in Brucella broth contai ning 1% agar under several conditions. Morphological conversion of individu al H. pylori on the agar plate was investigated with time after incubation under phase contrast microscopy. When H. pylori was inoculated in Brucella broth containing beta-cyclodextrin, the spiral form of the organism was obs erved even after 6 days of incubation under standard culture conditions: 37 degrees C, pH 7, and microaerobic atmosphere (5% O-2/10% CO2/85% N-2) (con trol). The morphological conversion of H. pylori was completed on day 3 in an aerobic atomosphere (20% O-2 supply) and on day 2 in an undermicroaerobi c atmosphere (<0.1% O-2). Its complete morphological conversion was observe d at pH 8 on day 5 and at pH 4 on day 6. All of the Ii. pylori (100%) incub ated at 20 degrees or 42 degrees C had converted from the bacillary to the coccoid form on day 4. Conditioned medium without beta-cyclodextrin caused complete conversion on day 5. These results suggest that organ concentratio n, pH, temperature, and beta-cyclodextrin may be related to the Ii. pylori morphological conversion from the bacillary to the coccoid form.