Ultrastructure of Helicobacter trogontum in culture and in the gastrointestinal tract of gnotobiotic mice.

Helicobacter trogontum is a micro-aerophilic urease-positive bacterium that has recently been isolated from the intestinal mucosa of rats. The purpose of this investigation was to study the ultrastructural details of this micro-organism in both pure culture and in the gastrointestinal tract of germ-free mice infected with H. trogontum. The micro-organism was a fusiform to slightly spiral gram-negative cell, 4-6 microm long and 0.6-0.7 microm wide, with four to seven bipolar sheathed flagella. The cytoplasm presented several irregular and also globular granules. On each side of the polar regions of the cells, there was a highly electron-dense band, the 'polar membrane'. Coccoidal forms were seen in old cultures. H. trogontum showed several ultrastructural characteristics of the Helicobacter genus and much resemblance to H. rappini and H. bilis. H. trogontum mainly colonised the large bowel of the gnotobiotic mice where it could be seen in the lumen and also inside the enterocytes. Vacuolation of the ileal epithelial cells, loss of microvilli and pronounced desquamation of the enterocytes of the caecum were observed in the bowel colonised by the bacterium. These observations raise the possibility that H. trogontum could cause some harm to the host at least in particular circumstances such as when it colonises the gastrointestinal tract of a germ-free host.