The first recorded mention in the annals of science of the name ‘bifidus’ as applied to a cell dates to 1900, when Tissier (1900) discovered in the faeces of breast-fed infants a rod-shaped, Gram-positive, non-gas-producing, anaerobic bacterium with bifid morphology which he termed Bacillus bifidus. At the beginning of the 20th century, Orla-Jensen, in a detailed paper on bacteria that produce lactic acid, classified the Bacillus bifidus as part of the Lactobacteriaceae family, and in 1924 he tried to propose it as a separate species, explaining that the various species of bifidobacteria “doubtless constitute a separate genus, possibly forming a connecting link between lactic acid bacteria and the propionic acid bacteria”. Although studies of this bacterial group gradually declined therafter, since 1950 there has been a flourish of new research that has brought the initial listing of Lactobacillus bifidus in the seventh edition of Bergey’s Manual of Determinative Bacteriology (Breed et al., 1957) to the present 24 species noted in its latest edition (Scardovi, 1986). Since then an additional five species have been described (B. gallicum, Lauer, 1990; B. gallinarum, Watabe et al., 1983; B. ruminantium and B. merycicum, Biavati and Mattarelli, 1991; B. saeculare, Biavati et al., 1991a).