Reclassification of "Propionibacterium rubrum" as P. jensenii.

The taxonomic relationship of strains previously designated as "Propionibacterium rubrum" to P. thoenii and P. jensenii was investigated by use of 16S ribosomal RNA sequence comparison, biochemical characteristics and DNA hybridization. A total of 46 strains representing the species P. jensenii and P. thoenii and the former species "P. rubrum" and also including 21 reference strains and 25 strains isolated from dairy sources were studied. The 16S rRNA sequence of strain "P. rubrum" CNRZ 85 (= ATCC 4871) was found to be almost identical to that of the type strain of P. jensenii. DNA hybridization data indicated that "P. rubrum" should belong to the species P. jensenii rather than P. thoenii, as formerly proposed. The "P. rubrum" strains should then be reclassified as a beta-haemolytic biovar of P. jensenii. The genomic species P. jensenii and P. thoenii could be differentiated by biochemical characteristics such as the production of acid from myo-inositol and starch.