A new phylogenetic group of Propionibacterium acnes

Immunofluorescence microscopy-based identification of presumptivePropionibacterium acnesisolates, using theP. acnes-specific mAb QUBPa3, revealed five organisms with an atypical cellular morphology. Unlike the coryneform morphology seen withP. acnestypes I and II, these isolates exhibited long slender filaments (which formed large tangled aggregates) not previously described inP. acnes. No reaction with mAbs that labelP. acnestypes IA (QUBPa1) and II (QUBPa2) was observed. Nucleotide sequencing of the 16S rRNA gene (1484 bp) revealed the isolates to have between 99.8 and 99.9 % identity to the 16S rRNA gene of theP. acnestype IA, IB and II strains NCTC 737, KPA171202 and NCTC 10390, respectively. Analysis of therecAhousekeeping gene (1047 bp) did reveal, however, a greater number of conserved nucleotide polymorphisms between the sequences from these isolates and those from NCTC 737 (98.9 % identity), KPA171202 (98.9 % identity) and NCTC 10390 (99.1 % identity). Phylogenetic investigations demonstrated that the isolates belong to a novelrecAcluster or lineage distinct fromP. acnestypes I and II. We now propose this new grouping asP. acnestype III. The prevalence and clinical importance of this novelrecAlineage amongst isolates ofP. acnesremains to be determined.