BackgroundBrachyspira pilosicoli is an anaerobic spirochaete that can colonizes the large intestine of many host species. Infection is particularly problematic in pigs and adult poultry, causing colitis and diarrhea, but it is also known to result in clinical problems in human beings. Despite the economic importance of the spirochaete as an animal pathogen, and its potential as a zoonotic agent, it has not received extensive study.MethodsA multilocus sequence typing (MLST) method based on the scheme used for other Brachyspira species was applied to 131 B. pilosicoli isolates originating from different host species and geographical areas. A variety of phylogenetic trees were constructed and analyzed to help understand the data.ResultsThe isolates were highly diverse, with 127 sequence types and 123 amino acid types being identified. Large numbers (50-112) of alleles were present at each locus, with all loci being highly polymorphic. The results of Shimodaira-Hasegawa tests identified extensive genetic recombination, although the calculated standardized index of association value (0.1568; P <0.0005) suggested the existence of some clonality. Strains from different host species and geographical origins generally were widely distributed throughout the population, although in nine of the ten cases where small clusters of related isolates occurred these were from the same geographical areas or farms/communities, and from the same species of origin. An exception to the latter was a cluster of Australian isolates originating from pigs, chickens and a human being, suggesting the likelihood of relatively recent transmission of members of this clonal group between species.ConclusionsThe strongly recombinant population structure of B. pilosicoli contrasts to the more highly clonal population structures of the related species Brachyspira hyodysenteriae and Brachyspira intermedia, both of which are specialized enteric pathogens of pigs and poultry. The genomic plasticity of B. pilosicoli may help to explain why it has been able to adapt to colonize the large intestines of a wider range of hosts compared to other Brachyspira species. The identification of a clonal group of isolates that had been recovered from different host species, including a human being, suggests that zoonotic transmission by B. pilosicoli may occur in nature. Evidence for local transmission between the same host species also was obtained.

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.Page 1 at all loci, but using the available data a total of 103 VNTR profiles were generated. 31The discriminatory power of this method was 0.976. A phylogenetic tree constructed 32 from the allelic profiles confirmed the diversity of B. pilosicoli, and the general lack 33 of clustering of strains based on species of origin or geographic origin. Some isolates 34 with known epidemiological links were found to be identical or highly similar. The 35 MLVA method was simple and easy to use, and could readily differentiate between 36 strains of B. pilosicoli. MLVA should prove to be a useful tool for rapid identification 37 of relationships between B. pilosicoli isolates in epidemiological investigations. 38

The anaerobic spirochaete Brachyspira pilosicoli colonizes the large intestine of birds and mammals, including human beings, and may induce colitis and diarrhoea. B. pilosicoli has a recombinant population structure, and strains show extensive genomic rearrangements and different genome sizes. The resident chromosomal gene bla OXA-63 in B. pilosicoli encodes OXA-63, a narrow-spectrum group IV class D b-lactamase. Genes encoding four OXA-63 variants have been described in B. pilosicoli, and the current study was designed to investigate the distribution and diversity of such genes and proteins in strains of B. pilosicoli. PCRs were used to amplify bla OXA-63 group genes from 118 B. pilosicoli strains from different host species and geographical origins. One primer set was targeted externally to the gene and two sets were designed to amplify internal components. A total of 16 strains (13.6 %) showed no evidence of possessing bla OXA-63 group genes, 44 (37.3 %) had a full gene, 27 (22.9 %) apparently had a gene but it failed to amplify with external primers, and 29 (24.6 %) had only one or other of the two internal components amplified. Based on translation of the nucleotide sequences, ten new variants of the b-lactamase, designated OXA-470 through OXA-479, were identified amongst the 44 strains that had the full gene amplified. The 16 strains lacking bla OXA-63 group genes had a region of 1674 bp missing around where the gene was expected to reside. Despite apparent genomic rearrangements occurring in B. pilosicoli, positive selection pressures for conservation of bla OXA-63 group genes and OXA proteins appear to have been exerted.

The article published in 2013 [1] described the use of the available Brachyspira multilocus sequence typing (MLST) scheme [2] to characterize the population structure of the intestinal spirochete Brachyspira pilosicoli. It used sequences of seven loci that were amplified from 131 strains that had been isolated from different geographical origins and species.

No abstract