Optimization of genotypic and biochemical methods to profile P. acnes isolates from a patient population

- The MALDI-TOF is a suitable method for P. acnes identification.
- 24 clinical strains have been clustered into phylogroups I (n = 21) and II (n = 3).
- Combination of PAtig gene and multiplex touchdown PCRs provides a fast typing.
- No clear relation was observed between antibiotic susceptibility and virulence.

Propionibacterium acnes is a key factor in the pathogenesis of acne vulgaris, although currently it is also being associated with medical-device infections. The aim of this work was to validate a safe and quick identification and typing of 24 clinical isolates of Propionibacterium acnes, applying a range of biochemical as well as genetic methods, and investigating the pathogenic potential to associate the different types with human health. RAPD-PCRs revealed the existence of two discernible clusters in correspondence with the phylogroups I and II, according to the PAtig gene polymorphism, leading them to be assigned as P. acnes subsp. acnes subsp. nov. Biotyping according to the pattern of sugar fermentation evidenced that all the isolates from acne and the majority from opportunistic infections fit the biotype I-B3. Consistent with the multiplex touchdown analysis, nearly all the isolates included in this biotype belonged to the subgroups IA1 (the exception being four strains classified as IB). The remaining ones were assigned to phylogroup II, considered to be part of the normal cutaneous microbiota. The susceptibility to three antibiotics was also investigated to explore the relations with the virulence, although no clear trend was identified.