Phenotypic and molecular characterization of Brachyspira spp. isolated from wild rodents

The occurrence of intestinal spirochaetes of genus Brachyspira in wild rodents was studied by cultivating 209 caecal samples. Spirochaetal cultures were obtained from 83% of rats and 33% of house mice. Biochemical characterization and six different species-specific PCR methods were applied to 101 of 118 isolates and a selection of 34 brachyspiras were further studied by sequencing of the 16S rRNA gene. The results showed that isolates representing all the established biochemical phenotypes could be cultured from the rodents, including the porcine pathogens Brachyspira hyodysenteriae and Brachyspira pilosicoli. Phylogenetic studies indicated that rodents carry Brachyspira spp. that are closely related to porcine and avian isolates, as well as variants previously not described. One group of hippurate-negative rat isolates were shown to possess the 16S rRNA gene hexa(T) nucleotide segment, previously described only in B. pilosicoli and 'Brachyspira corvi', and phylogenetically they formed a sister lineage of the B. pilosicoli cluster. Furthermore, a large number of the rodents were colonized by slowly growing, non- or weakly haemolytic spirochaetes. Most of these brachyspiras were isolated at 37°C and phylogenetically they formed two separate clusters. Sequence analysis of their 16S rRNA genes indicated that the new variants of Brachyspira spp. may constitute novel species of the genus Brachyspira.