Over a Decade of recA and tly Gene Sequence Typing of the Skin Bacterium Propionibacterium acnes: What Have We Learnt?

The Gram-positive, anaerobic bacterium forms part of the normal microbiota on human skin and mucosal surfaces. While normally associated with skin health, is also an opportunistic pathogen linked with a range of human infections and clinical conditions. Over the last decade, our knowledge of the intraspecies phylogenetics and taxonomy of this bacterium has increased tremendously due to the introduction of DNA typing schemes based on single and multiple gene loci, as well as whole genomes. Furthermore, this work has led to the identification of specific lineages associated with skin health and human disease. In this review we will look back at the introduction of DNA sequence typing of based on and loci, and then describe how these methods provided a basic understanding of the population genetic structure of the bacterium, and even helped characterize the grapevine-associated lineage of , known as type Zappe, which appears to have undergone a host switch from humans-to-plants. Particular limitations of and sequence typing will also be presented, as well as a detailed discussion of more recent, higher resolution, DNA-based methods to type and investigate its evolutionary history in greater detail.