Brachyspira pilosicoli colonization in experimentally infected mice can be facilitated by dietary manipulation

The Spirochete Brachyspira pilosicoli, Enteric Pathogen of Animals and Humans

Brachyspira pilosicoli is a slow-growing anaerobic spirochete that colonizes the large intestine. Colonization occurs commonly in pigs and adult chickens, causing colitis/typhlitis, diarrhea, poor growth rates, and reduced production. Colonization of humans also is common in some populations (individuals living in village and peri-urban settings in developing countries, recent immigrants from developing countries, homosexual males, and HIV-positive patients), but the spirochete rarely is investigated as a potential human enteric pathogen. In part this is due to its slow growth and specialized growth requirements, meaning that it is not detectable in human fecal samples using routine diagnostic methods. Nevertheless, it has been identified histologically attached to the colon and rectum in patients with conditions such as chronic diarrhea, rectal bleeding, and/or nonspecific abdominal discomfort, and one survey of Australian Aboriginal children showed that colonization was significantly associated with failure to thrive. B. pilosicoli has been detected in the bloodstream of elderly patients or individuals with chronic conditions such as alcoholism and malignancies. This review describes the spirochete and associated diseases. It aims to encourage clinicians and clinical microbiologists to consider B. pilosicoli in their differential diagnoses and to develop and use appropriate diagnostic protocols to identify the spirochete in clinical specimens.

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.

Evaluation of recombinant Brachyspira pilosicoli oligopeptide-binding proteins as vaccine candidates in a mouse model of intestinal spirochaetosis

The anaerobic intestinal spirochaete Brachyspira pilosicoli colonizes the large intestine of humans, and various species of animals and birds, in which it may induce a mild colitis and diarrhoea. The aim of the current study was to evaluate the use of putative oligopeptide-binding proteins of B. pilosicoli as vaccine components. A partial genome sequence of B. pilosicoli porcine strain 95/1000 was subjected to bioinformatics analysis, and six genes predicted to encode oligopeptide-binding proteins were selected. Following a PCR-based distribution study of the genes across different strains of the spirochaete, they were amplified from B. pilosicoli human strain WesB and cloned in Escherichia coli. The recombinant histidine-tagged proteins were purified and subjected to in vitro and in vivo immunogenicity analysis. Recombinant products (P-1 and P-3) from two genes that were immunogenic and recognized by sera from pigs that had recovered from B. pilosicoli infections were tested in a mouse model of intestinal spirochaetosis. For each recombinant protein, groups of 12 C3H/HeJ mice were vaccinated subcutaneously with 100 microg protein emulsified in Freund's incomplete adjuvant, twice with a 2 week interval. Two weeks later the vaccinated and non-vaccinated control animals were challenged orally with B. pilosicoli strain WesB. Both proteins induced systemic and local colonic IgG antibody responses, and, following experimental infection, the cumulative number of colonization days was significantly (P<0.001) less in both groups of vaccinated mice compared to the control mice. There were significantly (P=0.012) fewer mice colonized in the group vaccinated with P-1 than in the non-vaccinated control group. The results suggest that oligopeptide-binding proteins may have potential for use as components of vaccines for B. pilosicoli.

The histological features of intestinal spirochetosis in a series of 113 patients

A multicenter retrospective review of cases diagnosed as spirochetosis was performed to determine the presenting symptoms and histological changes. A total of 113 cases were retrieved from the archives, consisting of 97 colorectal specimens and 16 appendices. In only 25 cases was the presenting symptom recorded as diarrhea. Of the colorectal specimens, 87 (90%) showed no mucosal abnormality (apart from the spirochetes); the other 10 showed mucosal inflammation but 6 of them had a diagnosis of another inflammatory disease process accounting for the inflammatory changes. Five appendices showed acute appendicitis; the other 11 were unremarkable. It is concluded that spirochetosis in an unselected general population is unlikely to be of pathological significance. Furthermore, if spirochetosis is observed in an inflamed biopsy, it is most likely to be an incidental finding.

Colonic spirochetosis in animals and humans

Colonic spirochetosis is a disease caused by the gram-negative bacteria Brachyspira aalborgi and Brachyspira pilosicoli. B. pilosicoli induces disease in both humans and animals, whereas B. aalborgi affects only humans and higher primates. Symptoms in humans include diarrhea, rectal bleeding, and abdominal cramps. Colonic spirochetosis is common in third world countries; however, in developed countries, the disease is observed mainly in homosexual males. Terminally ill patients infected with Brachyspira are particularly at risk for developing spirochetemia. Diarrhea, poor growth performance, and decreased feed-to-gain efficiency is seen in pigs with colonic spirochetosis. The disease in chickens is characterized by delayed and/or reduced egg production, diarrhea, poor feed conversion, and retarded growth. Thus, colonic spirochetosis can represent a serious economic loss in the swine and poultry industries. The organisms are transmitted by the fecal-oral route, and several studies have demonstrated that human, primate, pig, dog, or bird strains of B. pilosicoli can be transmitted to pigs, chickens, and mice. B. pilosicoli may be a zoonotic pathogen, and although it has not been demonstrated, there is a possibility that both B. pilosicoli and B. aalborgi can be transferred to humans via contact with the feces of infected animals, meat from infected animals, or food contaminated by food handlers. Neither B. pilosicoli nor B. aalborgi has been well characterized in terms of basic cellular functions, pathogenicity, or genetics. Studies are needed to more thoroughly understand these Brachyspira species and their disease mechanisms.