The pathogenic intestinal spirochaete Brachyspira pilosicoli forms a diverse recombinant species demonstrating some local clustering of related strains and potential for zoonotic spread

Abstract

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.

Molecular Epidemiology of Novel Pathogen “Brachyspira hampsonii” Reveals Relationships between Diverse Genetic Groups, Regions, Host Species, and Other Pathogenic and Commensal Brachyspira Species

“…It is interesting to note that although B. intermedia and particularly B. pilosicoli have a similar number of STs as they have AATs (23, 24), B. hyodysenteriae shows a lower number of AATs compared to STs (5). It is thought that the high plasticity, recombination, and genetic diversity of B. pilosicoli may contribute to its ability to infect and cause disease in multiple host species, including swine, chicken, and human beings (23). This is in contrast to B. hyodysenteriae that shows a strong clonal distribution in a diverse population and is known to cause disease most often in swine (5).…”

“…Multilocus sequence typing (MLST) is a high-resolution method that uses nucleotide sequence differences between conserved housekeeping genes to characterize and differentiate genotypes of a pathogen (19). This technique has been used for local and global molecular epidemiological studies of various Brachyspira species (20), including B. hyodysenteriae (5,21,22), Brachyspira pilosicoli (23), Brachyspira intermedia (24), Brachyspira murdochii, and Brachyspira innocens (25), thus warranting its application for the characterization of B. hampsonii.…”

Antimicrobial Susceptibility Patterns of Brachyspira Species Isolated from Swine Herds in the United States

“…1 and 2). Furthermore, B. pilosicoli, which is known to be a highly recombinant species that demonstrates a substantial amount of genomic variation (40), could be prone to developing mutations associated with antimicrobial resistance. The tendency of B. pilosicoli to develop resistance more rapidly than other Brachyspira species is supported by the "skipped well" phenomenon, i.e., spontaneous mutations associated with in vitro resistance to an antimicrobial that develops in the inoculated medium during susceptibility testing (36).…”

Genes encoding ten newly designated OXA-63 group class D β-lactamases identified in strains of the pathogenic intestinal spirochaete Brachyspira pilosicoli

“…The spirochaete has a recombinant population structure (Trott et al, 1998;Neo et al, 2013), and genomic sequencing has revealed that strains show extensive genomic rearrangements and that their genome sizes vary (Wanchanthuek et al, 2010;Mappley et al, 2012;Lin et al, 2013). Infection with B. pilosicoli occurs commonly in intensively housed pigs and adult poultry, and also in human beings living in crowded conditions in developing countries (Trott et al, 1997;Mikosza & Hampson, 2001;Margawani et al, 2004).…”