Helicobacter--species classification and identification.

The genus Helicobacter was created in 1989 with H. pylori as the type species. Since then the genus has expanded to include about 18 species. Some species were reclassified from Campylobacter, but most were newly discovered microorganisms from gastric or intestinal sites in mammalian host animals. The essential property of almost all helicobacters is the presence of sheathed flagella. Most species possess strong ureolytic ability, particularly those associated with gastric mucosa, and exhibit considerable diversity in cell morphology with respect to cell length, number and location of flagella, and presence of periplasmic fibrils. H. pylori has a global distribution and infects human gastric mucosa exclusively but there is some evidence for infection in cats. Genomes of isolates from different individuals are unusual in their diversity in gene order and sequences within individual genes. 'H. heilmannii' is another gastric spiral shaped organism less frequently infecting humans but commonly found in cat and dog gastric tissue. H. felis is important in the mouse model of infection. A range of conventional phenotypic tests as well as some new PCR based assays are available for identifying isolates of Helicobacter from clinical specimens.