Unification of Bifidobacterium infantis and Bifidobacterium suis as Bifidobacterium longum

This study examined the taxonomic relationships between three Bifidobacterium species: B. infantis, B. longum, and B. suis using multiple molecular methods. Researchers analyzed 25 bacterial strains isolated from human and pig feces through carbohydrate fermentation patterns, DNA-DNA hybridization, ribotyping, and random amplified polymorphic DNA-PCR (RAPD-PCR). DNA-DNA hybridization results showed 67-85% relatedness among the three species under both optimal (42°C) and stringent (52°C) conditions, exceeding the 70% threshold for species classification. While carbohydrate fermentation patterns varied considerably among strains, molecular methods (ribotyping and RAPD-PCR) consistently distinguished three distinct genetic groups. Based on these findings, the authors concluded that B. infantis and B. suis should be unified with B. longum as a single species, with the three groups recognized as distinct biotypes: the infantis type, longum type, and suis type. This taxonomic revision reflects the high genetic similarity among these bacteria and demonstrates that molecular methods are more reliable than traditional biochemical characteristics for bacterial classification.

Key findings

• DNA-DNA hybridization showed 67-85% relatedness among B. infantis, B. longum, and B. suis strains, exceeding the 70% threshold for single species classification.
• Ribotyping and RAPD-PCR analysis successfully distinguished three distinct genetic groups within the strains, despite variable carbohydrate fermentation patterns.
• Carbohydrate fermentation patterns were unreliable for species differentiation due to variations among isolates independent of species designation.
• B. infantis and B. suis should be unified as B. longum, divided into three biotypes based on molecular methods rather than biochemical characteristics.