Proposal to reclassify the three biotypes of Bifidobacterium longum as three subspecies: Bifidobacterium longum subsp. longum subsp. nov., Bifidobacterium longum subsp. infantis comb. nov. and Bifidobacterium longum subsp. suis comb. nov.

In the year 2002, Bifidobacterium longum, Bifidobacterium infantis and Bifidobacterium suis were unified into a single species, Bifidobacterium longum, preserving the former species names through the creation of the three biotypes 'longum', 'infantis' and 'suis'. Consequently, the use of the species names B. infantis and B. suis was to be discontinued. The above taxonomic rearrangement of B. longum was based on DNA-DNA hybridizations and 16S rRNA and HSP60 gene sequence analysis. However, a variety of other genotypic techniques including ribotyping, amplified rDNA restriction analysis (ARDRA), randomly amplified polymorphic DNA (RAPD)-PCR, BOX-PCR, PCR-denaturing gradient gel electrophoresis (DGGE), comparison of the recA, tuf and ldh gene sequences, plasmid profiling and considerable variation in carbohydrate fermentation patterns as well as results of starch and PAGE electrophoresis experiments clearly discriminate former B. longum, B. infantis and B. suis strains. In the present paper we compile this published information and propose the description of Bifidobacterium longum subsp. longum subsp. nov., Bifidobacterium longum subsp. infantis comb. nov. and Bifidobacterium longum subsp. suis comb. nov. The International Committee on Systematics of Prokaryotes Subcommittee on the taxonomy of Bifidobacterium, Lactobacillus and related organisms is in favour of this proposal. The type strains of Bifidobacterium longum subsp. longum subsp. nov., subsp. infantis comb. nov. and subsp. suis comb. nov. are E194b (variant a)T (ATCC 15707T=DSM 20219T), S12T (=ATCC 15697T=DSM 20088T) and Su859T (ATCC 27533T=DSM 20211T), respectively.