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

1 Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, University of Ghent, Salisburylaan 133, B-9820 Merelbeke, Belgium 2 Delft Diagnostic Laboratory, R. de Graafweg 7, 2600 GA, Delft, The Netherlands 3 Department of Food and Environmental Hygiene, Faculty of Veterinary Medicine, University of Helsinki, PO Box 57, 00014 Helsinki, Finland 4 Department of Microbiology, Faculty of Sciences, University of Ghent, Ledeganckstraat, B-9000 Ghent, Belgium Author for correspondence: Dominic De Groote. Tel: +32 9 264 77 45. Fax: +32 9 264 77 89. e-mail: dominic.degroote{at}rug.ac.be ABSTRACT ‘ Gastrospirillum suis ’ is an uncultured, tightly spiral micro-organism that has been associated with ulcer disease in the stomachs of pigs. It was the purpose of this study to determine the phylogenetic position of ‘ G. suis ’. Stomachs of five slaughterhouse pigs, originating from different Belgian and 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 broadrange primers and five helicobacter-like sequences were determined either by direct or indirect sequence analysis. An inter-sequence homology of 99·7% was observed, suggesting that the sequences originated from strains belonging to a single species. Phylogenetic analysis of the consensus sequence placed the organism within the genus Helicobacter , where it formed a distinct sub-group together with other gastrospirillum-like bacteria ( Helicobacter felis, Helicobacter bizzozeronii, Helicobacter salomonis and ‘ Helicobacter heilmannii ’ types 1 and 2). Diagnostic PCR primers and a probe were developed that differentiated the porcine sequences from all known helicobacters. These results indicate that the porcine sequences represent a single taxon within the genus Helicobacter . The low similarity level towards H. salomonis (96·6%), its closest validly named neighbour, strongly suggests that this taxon is a novel Helicobacter species. In situ hybridization experiments linked 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. Key Words: Helicobacter • ‘ Gastrospirillum suis ’ • pig • stomach • PCR The GenBank accession number for the 16S rDNA nucleotide reference sequence of ‘ Candidatus Helicobacter