'Candidatus Helicobacter suis', a gastric helicobacter from pigs, and its phylogenetic relatedness to other gastrospirilla

'Gastrospirillum suis' is an uncultured, tightly spiral micro-organism that has been associated with ulcer disease in the stomachs or pigs. Ir was me purpose of this study to determine the phylogenetic position of 'G. suis'. Stomachs of five slaughterhouse pigs, originating from different Belgian an d Dutch farms, were selected on the basis of the presence of 'G. suis'-like bacteria, as demonstrated by biochemical, immunohistochemical and electron microscopical data. Bacterial 16S rDNA was amplified by PCR using broad-ra nge primers and five helicobacter-like sequences were determined either by direct or indirect sequence analysis. An inter-sequence homology of 99.7% w as observed, suggesting that the sequences originated from strains belongin g to a single species. Phylogenetic analysis of the consensus sequence plac ed the organism within the genus Helicobacter, where it formed a distinct s ub-group together with other gastrospirillum-like bacteria (Helicobacter fe lis, Helicobacter bizzozeronii, Helicobacter salomonis and 'Helicobacter he ilmannii' types 1 and 2). Diagnostic PCR primers and a probe were developed that differentiated the porcine sequences from all known helicobacters. Th ese results indicate that the porcine sequences represent a single taxon wi thin the genus Helicobacter. The low similarity level towards H. salomonis (96.6%), its closest validly named neighbour, strongly suggests that this t axon is a novel Helicobacter species. In situ hybridization experiments lin ked the reference sequence to the 'G. suis'-like bacteria. On the basis of these results, we propose the name 'Candidatus Helicobacter suis' for this gastric helicobacter from pigs.