Examination of Serpulina pilosicoli for attachment and invasion determinants of Enterobacteria

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.

The intestinal spirochete Brachyspira pilosicoli attaches to cultured Caco-2 cells and induces pathological changes

BACKGROUND

Brachyspira pilosicoli is an anaerobic spirochete that has received relatively little study, partly due to its specialized culture requirements and slow growth. This bacterium colonizes the large intestine of various species, including humans; typically, a dense layer of spirochete cells may be found intimately attached by one cell end to the surface of colonic enterocytes. Colonized individuals may develop colitis, but the mechanisms involved are not understood. The current study aimed to develop an in vitro model to investigate this process.

METHODOLOGY/PRINCIPAL FINDINGS

Four strains of B. pilosicoli were incubated at a high multiplicity of infection with monolayers of a human colonic adenocarcinoma cell line (Caco-2 cells). One strain isolated from a pig (95/1000) and one from a human (WesB) attached to the monolayers. Colonization increased with time, with the Caco-2 cell junctions being the initial targets of attachment. By electron microscopy, individual spirochete cells could be seen to have one cell end invaginated into the Caco-2 cell membranes, with the rest of the spirochete draped over the Caco-2 cell surface. After 6 h incubation, the monolayer was covered with a layer of spirochetes. Colonized monolayers demonstrated a time-dependent series of changes: staining with labelled phalloidin identified accumulation of actin at the cell junctions; ZO-1 staining revealed a loss of Caco-2 tight junction integrity; and Hoechst staining showed condensation and fragmentation of nuclear material consistent with apoptosis. Using quantitative reverse transcription PCR, the colonized monolayers demonstrated a significant up-regulation of interleukin-1beta (IL-1beta) and IL-8 expression. B. pilosicoli sonicates caused significant up-regulation of IL-1beta, TNF-alpha, and IL-6, but culture supernatants and non-pathogenic Brachyspira innocens did not alter cytokine expression.

CONCLUSIONS/SIGNIFICANCE

The changes induced in the Caco-2 cells provide evidence that B. pilosicoli has pathogenic potential, and give insights into the likely in vivo pathogenesis.

Comparative pathology and pathogenesis of naturally acquired and experimentally induced colonic spirochetosis

Research in the past decade has led to the recognition ofBrachyspira(formerlySerpulina)pilosicolias the primary etiologic agent of colonic spirochetosis (CS), an emerging cause of colitis in humans and animals. Attachment of spirochetes to the epithelial surface of the lower intestine is considered to be the hallmark of CS. However, becauseB. pilosicoli, B. aalborgiand unclassified flagellated bacteria are found singly or together in humans and non-human primates with CS lesions, attachment of spiral-shaped bacteria may not represent the same etiopathogenetic entity in all hosts. Moreover, North American opossums with CS are infected withB. aalborgi-like spirochetes together with flagellated bacteria, whereasB. pilosicoliis found alone in dogs, pigs, chickens and other species of birds with CS. Conversely, guinea-pigs with CS have unidentified spirochetes that may beB. pilosicoli or B. aalborgi.The pig model of CS suggests that attachment ofB. pilosicolito epithelial cells may be transient. By contrast, persistence ofB. pilosicoliin the cecal and colonic crypt lumina, chronic inflammation caused by spirochetal invasion into the subepithelial lamina propria and translocation to extraintestinal sites may be more important than previously thought. This review describes the lesions seen in naturally occurring and experimentally induced CS of animals, and it sets the stage for future research into the pathogenic mechanisms of infection and colitis caused byB. pilosicoli.

Human intestinal spirochetosis:Brachyspira aalborgiand/orBrachyspira pilosicoli?

Intestinal spirochetosis in humans (HIS) is a condition defined by the presence of a layer of spirochetes attached by one cell end to the colorectal epithelium. The pathologic significance of HIS is uncertain, but it has been linked to chronic diarrhea and other abdominal complaints. Two anaerobic intestinal spirochete species have been associated with HIS, namelyBrachyspira pilosicoliandBrachyspira aalborgi.Brachyspira pilosicoli, which colonizes many animal species, is common (~30%) in the feces of people from developing countries, including Australian Aborigines, and in HIV+ patients and male homosexuals in Western societies. It is also commonly seen attached to the rectal mucosa of homosexual males. In other groups in Western societies both the presence of B.pilosicoliin feces and histologic HIS are uncommon (~1.5%).Brachyspira aalborgiis an extremely slow growing and fastidious spirochete, which previously had been isolated from an HIS patient in Denmark. Recent studies using polymerase chain reaction amplification of DNA from intestinal biopsies from a series of cases of HIS in the general Western population demonstrated thatB. aalborgi, rather thanB. pilosicoli, was the main spirochete species involved in these patients. This review outlines recent developments in the study of HIS and the two spirochete species, and identifies priorities for future research.

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.