Cloning and DNA sequence analysis of an immunogenic glucose-galactose MglB lipoprotein homologue from Brachyspira pilosicoli, the agent of colonic spirochetosis.

Colonic spirochetosis (CS) is a newly emerging infectious disease of humans and animals caused by the pathogenic spirochete Brachyspira (formerly Serpulina) pilosicoli (6, 7, 9, 38, 56, 58). Infection with B. pilosicoli or lesions consistent with CS have been recorded in a wide variety of hosts including human beings (6, 22, 56, 61, 62), nonhuman primates (8, 9, 36), pigs (2, 6, 7, 11, 13, 27, 52, 54, 55), dogs (6, 8, 10), commercial chickens, and various species of wild and zoo birds (39). The prevalence of CS among adults in the United States and Europe ranges between 4.5 and 32.2% (45). By contrast, infection with B. pilosicoli is endemic among villagers in Papua New Guinea; 93.6% of the population is infected for a calculated average duration of about 4 months (61). Porcine, canine, human, and monkey strains of B. pilosicoli are closely related and cause CS in chick and swine infection models (6, 9, 10, 11, 15, 35, 36, 54, 57–60). Similarly, laboratory mice can be colonized for up to 30 days with human, porcine, and avian B. pilosicoli strains (46). Collectively, these data suggest that B. pilosicoli may be zoonotic, and this has public health significance. By analogy with the pathogenic intestinal spirochete of swine Brachyspira hyodysenteriae, initial colonization of the colon by B. pilosicoli appears to involve motility-regulated mucin association (24, 33, 64). Multiplication of the spirochetes in close proximity with the mucosal surface and inside the lumina of the crypts (54) is followed by intimate attachment along the apical membrane of enterocytes causing effacement of microvilli (7, 8, 11, 37, 52, 56, 57, 59). Comparative studies with cultured enterocytes and infection models suggest a specific spirochete ligand-host cell membrane receptor interaction during intimate attachment of B. pilosicoli (35, 36). Penetration of the colonic epithelium and invasion of B. pilosicoli into the submucosal connective tissue are seen in humans, pigs, and dogs with naturally occurring disease and in experimentally infected pigs and chicks (8, 35). Translocation of B. pilosicoli to extraintestinal sites including the bloodstreams of terminally ill human patients also has been documented (62). Because B. pilosicoli is emerging as a human pathogen and because these organisms have not been studied in detail, there is a need to more fully understand basic mechanisms involved in intestinal colonization and disease. Considerable genetic information for the pathogenic spirochetes Borrelia burgdorferi, the cause of Lyme disease (16), and Treponema pallidum, the syphilis spirochete (17), is available. With the exception of the role of NADH oxidase expression in colonization of the swine colon by B. hyodysenteriae (51) and of flagellar gene expression in the motility of B. hyodysenteriae (25, 44) and the oral spirochete Treponema denticola (28), little is known about the structure-function relationship of specific gene products in the pathogenesis of spirochetal diseases. We have shown that swine that recovered from CS develop serum immunoglobulin G (IgG) antibodies to several B. pilosicoli antigens (65; P. Zhang, X. Cheng, M. Mathiesen, and G. E. Duhamel, Abstr. 79th Annu. Meet. Conf. Res. Workers Anim. Dis., abstr. 54, 1998). The purpose of this study was to characterize an antigen recognized by antibodies present in sera obtained from pigs that recovered from CS. The present communication describes the cloning, sequencing, and expression of a mglB gene homologue (encoding a protein formerly known as β-methylgalactoside) in B. pilosicoli. (This report represents a portion of a thesis submitted by P. Zhang to the University of Nebraska in partial fulfillment of the requirements for the Ph.D. degree.)