The anaerobic skin colonizer Staphylococcus saccharolyticus, a possible agent of prosthetic joint infections, exhibits excessive genome decay

Human skin-colonizing bacteria can have double ‘personalities’, which muddles the distinction between commensals and pathogens. Coagulase-negative staphylococci (CoNS) are part of the normal skin microbiota, but some CoNS species can act as opportunistic pathogens.

The anaerobic CoNS species Staphylococcus saccharolyticus has not received much attention, although it is a frequent colonizer of human skin and associated with prosthetic joint infections. Therefore, we determined the frequencies of S. saccharolyticus on human skin and analyzed clinical and skin-derived S. saccharolyticus strains by genome sequencing and biochemical tests.

Analysis of skin samples from volunteers identified S. saccharolyticus on the forehead and in the elbow pit in approx. 20% of the samples. Genome sequencing revealed an unexpected feature of S. saccharolyticus: extensive genome decay, with over 300 pseudogenes, indicating ongoing reductive evolution. Many genes of the core metabolism are not functional, rendering the species auxotrophic for several amino acids, which could explain its slow growth, and the need for fastidious growth conditions.

In an attempt to evaluate the virulence potential of S. saccharolyticus, we determined abundantly secreted proteins: these included stress response proteins such as heat shock- and oxidative stress-related factors, as well as immunodominant staphylococcal surface antigens. The strains secrete lipases and a hyaluronic acid lyase; hyaluronidase as well as urease activities were detected with biochemical assays.

Our study revealed that S. saccharolyticus has adapted its genome, possibly due to a recent change of habitat; moreover, the data imply that the species has tissue-invasive potential and might cause prosthetic joint infections.