To identify bacterial traits related to adhesion ability in human bifidobacteria, 13 strains of Bifidobacterium longum isolated from human gastric juice and intestine were studied. Strains were tested for their capability to adhere to Caco‐2 cells and classified as adhesive (Adh+) or non‐adhesive (Adh–). Adh+ and Adh– strains were then investigated for their autoaggregation ability and surface hydrophobicity. Comparing the properties of Adh+ and Adh–, we observed that strains were able to adhere to cell monolayers if they autoaggregate and manifest a good degree of hydrophobicity as determined by microbial adhesion to hydrocarbons. These two traits could be used for preliminary screening to identify potentially adherent isolates.

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A total of 1461 bacterial isolates, representing 24 different species of the genus Bifidobacterium, were examined for the presence of plasmid DNA. Approximately 20% of the isolates contained detectable plasmids, but only four species were presented: B. longum, the predominant bifid species in the human intestine; B. globosum, the most common in animals; and B. asteroides and B. indicum, species found exclusively in the intestines of western and asiatic honey bees, respectively. Multiple plasmids were common among isolates of B. longum and B. asteroides, while all plasmid-bearing isolates of B. globosum and 60% of B. indicum isolates contained only one plasmid each. Certain multiple plasma profiles were predominant among the B. longum and B. asteroides isolates.

On the basis of autoaggregation ability, two different phenotypes (Agg+ and Agg-) were selected from a strain (BSu895) of Bifidobacterium suis. The relationship between autoaggregation and adhesion of bacteria to intestinal tissue was investigated by observing the adhesivity of the two phenotypic variants to ileum and colon tissue pieces collected from six new-born piglets. The results suggest that there is a good relationship between autoaggregation and adhesion as variant Agg+ (autoaggregating) has a stronger adhesion ability than Agg- (non-autoaggregating).