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Curr Opin Microbiol. 1998 Feb;1(1):96-102.

Helicobacter pylori: molecular evolution of a bacterial quasi-species.

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Department of Molecular Biology, Immunobiological Research Institute ofSiena (IRIS), Chiron Vaccines, Via Fiorentina 1, 53100 Siena, Italy.


Helicobacter pylori persists chronically within individuals and as they spread the mutating bacteria migrate with them. The continuous selection and microevolution generates a population of closely related but different bacteria that behave like a quasi-species. Within this heterogeneity, H. pylori strains fall into distinct types, into the virulent (type I) and less virulent (type II) strains, based on the presence of a pathogenicity island (cag) that encodes a specialized secretion machinery. We propose that during chronic infection a dynamic equilibrium between bacteria expressing a disparate degree of virulence is established, and that diverse forms prevail at different times.

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