Emendation of Propionibacterium acnes subsp. acnes (Deiko et al. 2015) and proposal of Propionibacterium acnes type II as Propionibacterium acnes subsp. defendens subsp. nov

Recently, strains of Propionibacterium acnes from the type III genetic division have been proposed as Propionibacterium acnes subsp. elongatum subsp. nov., with strains from the type I and II divisions collectively classified as Propionibacterium acnes subsp. acnes subsp. nov. Under such a taxonomic re-appraisal, we believe that types I and II should also have their own separate rank of subspecies. In support of this, we describe a polyphasic taxonomic study based on the analysis of publically available multilocus and whole genome sequence datasets, alongside a systematic review of previously published phylogenetic, genomic, phenotypic and clinical data. Strains of types I and II form highly distinct clades based on multilocus sequence analysis (MLSA) and whole genome phylogenetic reconstructions. In silico or digital DNA-DNA similarity values also fall within the 70-80% boundary recommended for bacterial subspecies. Furthermore, we see important differences in genome content, including the presence of an active CRISPR/Cas system in type II strains, but not type I, and evidence for increasing linkage equilibrium within the separate divisions. Key biochemical differences include positive tests for -haemolytic, neuraminidase and sorbitol fermentation activities with type I strains, but not type II. We now emend the description of Propionibacterium acnes subsp. acnes (Deiko et al. 2015) and propose type II as Propionibacterium acnes subsp. defendens subsp. nov. The type strain of Propionibacterium acnes subsp. defendens subsp. nov. is ATCC 11828 (=JCM 6473=CCUG 6369).