Polymorphism of Genes Associated with Putative Fimbriae of Bifidobacterium longum Strains, with Specific Reference to Their Host Specific Colonization

The polymorphism of a length of DNA including several genes encoding putative mucosal glycoprotein binding fimbriae－associated proteins （the putative fimbriae region） of Bifidobaeterium longum was investigated with specific reference to its host specific colonization. PCR－restriction fragment length polymorphism （RFLP） assays were performed on 44 clonally different strains that had been isolated from fecal samples collected from 12 Japanese subjects over a 15－month period. The assays revealed that the putative fimbriae region is highly heterogeneous, with only a limited number of strains sharing the same RFLP fragment pattern. However, fragment patterns observed for the adjacent up－ and down－stream DNA regions not associated with the fimbriae shared the same fragment patterns in many strains, further highlighting the polymorphic nature of the putative fimbriae region. A dendrogram created of the fragment patterns of the putative fimbriae region showed 5 genotypes at the 70％ similarity level, and 4 of the genotypes were further subdivided at the 80％ similarity level into 9 sub－genotypes, in which at least half of the strains isolated from each host belonged to the same sub－genotype. The evidence suggests that fimbriae of B. longum are closely associated with the host－specific intestinal colonization. If this is the case, probiotic use of B. longum strains indigenous to the host may be more effective for the promotion and maintenance of that individual’s health.