Phylogenetic evidence for novel and genetically different intestinal spirochetes resembling Brachyspira aalborgi in the mucosa of the human colon as revealed by 165 rDNA analysis

intestinal spirochetes (Brachyspira spp.) are causative agents of intestina l disorders in animals and humans. Phylogenetic analysis of cloned 16S rRNA genes from biopsies of the intestinal mucosa of the colon from two Swedish 60-years old adults without clinical symptoms revealed the presence of int estinal spirochetes. Seventeen clones from two individuals and 11 reference strains were analyzed and the intestinal spirochetes could be divided into two lineages, the Brachyspira aalborgi and the Brachyspira hyodysenteriae lineages. All of the clones grouped in the B. aalborgi lineage. Moreover, t he B. aalborgi lineage could be divided into three distinct phylogenetic cl usters as confirmed by bootstrap and signature nucleotide analysis. The fir st cluster comprised 6 clones and the type strain B. aalborgi NCTC 11492(T) . The cluster 1 showed a 16S rRNA gene similarity of 99.4-99.9%. This clust er also harbored che only other strain of B. aalborgi isolated so far, name ly strain W1, which was subjected to phylogenetic analysis in this work. Th e second cluster harbored 9 clones with a 98.7 to 99.5% range of 16S rDNA s imilarity ro the B. aalborgi cluster 1. Two clones branched distinct and ea rly of the B. aalborgi, line forming the third cluster and was found to be 98.7% similar to cluster 1 and 98.3-99.1% to cluster 2. Interestingly, this shows that considerable variation of intestinal spirochetes can be found a s constituents of the colonic microbiota in humans, genetically resembling B. aalborgi. The presented data aid significantly to the diagnostic and tax onomic work on these organisms.