The Spirochete Brachyspira pilosicoli, Enteric Pathogen of Animals and Humans

Abstract

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.

Keywords: Brachyspira; animals; colitis; control; diagnosis; epidemiology; spirochete; zoonosis.

FIG 1

Appearance of motile, flexuous, thin, spiral-shaped cells of B. pilosicoli as observed under a phase-contrast microscope.

FIG 2

Appearance of a “false brush border” of Brachyspira pilosicoli cells attached by one cell end to the luminal surface of human colonic enterocytes in a patient diagnosed with HIS.

FIG 3

Scanning electron microscope image of B. pilosicoli cells attached by one cell end to a monolayer of cultured Caco-2 cells.

FIG 4

Scanning electron microscope image of dense fields of B. pilosicoli cells attached by one cell end to the luminal surface of the colon in an experimentally infected pig.

FIG 5

Appearance of the luminal surface of the opened colon of a pig experimentally infected with B. pilosicoli. The exposed mucosa shows congestion and hyperemia, with focal areas of superficial mucosal erosions and hemorrhages tracking along the length of the colon.

FIG 6

Appearance of the luminal surface of an opened cecum of an adult laying chicken infected with B. pilosicoli. The exposed mucosa is covered by mucoid tan content. Areas of congestion, focal erosions, and hemorrhage can be seen in the mucosa underneath the contents.

FIG 7

In situ hybridization with a labeled oligonucleotide probe specific to B. pilosicoli, showing localized attachment of a fringe of fluorescing spirochete cells to the surface of colonocytes in an infected pig.