16S rRNA gene sequences of ‘Candidatus Campylobacter hominis’, a novel uncultivated species, are found in the gastrointestinal tract of healthy humans

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Abstract
Although some Campylobacter species are agents of gastroenteritis and periodontal disease in humans, little is known of the variety of campylobacters in the gastrointestinal tract of healthy individuals. This paper provides evidence for the existence of a previously undescribed, uncultivated Campylobacter species that may be a commensal in the healthy human gut. Saliva and faeces from 20 healthy individuals were examined by PCR assays specific for nine species of campylobacter (C. sputorum, C. concisus, C. upsaliensis, C. helveticus, C. Iari, C. fetus, C. hyointestinalis, C. jejuni and C. coli) and for the genus as a whole. Genus-specific amplicons were produced from 19 of 20 saliva samples and from 18 of 20 faecal samples. C. concisuss species-specific amplicons were produced from 19 of 20 saliva samples and 3 of 20 faecal samples. The faecal samples were all PCR-negative for other Campylobacter species. Three unidentified 16S rRNA Campylobacter genus-specific amplicons of faecal origin were sequenced. Phylogenetic analysis showed that these sequences were 99% similar, and clustered within the genus as a novel group which was termed HS (HS = healthy subject). A PCR primer pair specific for the HS group was designed from the sequence data and used to reexamine the original samples. Although it was not possible to culture the organism from faeces, specific PCR assay detected it in 10 of the 20 faecal samples, but not in any corresponding saliva samples. The authors propose that the source of the amplicons is a previously undescribed and so far uncultivated species, which they term ‘Candidatus Campylobacter hominis’.