RESUMEN
More than 50% of the world's population is infected with Helicobacter pylori (H. pylori) - a Gram negative bacterium, which persists in the human stomach and duodenum, causing gastric or duodenal ulcers and gastric cancer. The majority of H. pylori cells demonstrate rod-shape morphology occurring in two subtypes: spiral and S-shaped. Both are isolated from mucus layer biopsy specimens of the stomach or from short-term cultures. However, results obtained from electron microscopy revealed that H. pylori long-term cultures not only consist of classic, spiral shaped bacteria, but also contain alternative forms of coccoid cells. Further investigations showed that coccoid forms of H. pylori may be divided into two types: viable but non-culturable coccus (VBnC) and a degenerative form, coccoid stage which is probably the effect of bacterial cell death. Transformation from spiral to coccoid form is induced under stress conditions, such as the presence of antibiotics. But still there is no evidence for reversion from the coccoid state to the viable and infectious spiral form. Besides the planktonic form, H. pylori also forms homo-, and heterogenic biofilms, which may constitute a potential environmental reservoir of this bacterium. The antigenic repertoire and the immunomodulatory and infectious properties of different H. pylori forms differ greatly. The variation in those properties suggests that morphological forms of H. pylori are potentially involved in the transmission of the infection. This review presents recent findings on the variability, antigenicity and infectious properties of H. pylori morphological forms and their potential role in the transmission of the infection.