Are Staphylococcus aureus fracture-related infections clonal, and what are the implications for bacteriophage...

Fracture related infections (FRI) are a devastating complication of orthopedic trauma care, most commonly caused by Staphylococcus aureus. The organisms' ability to form biofilms complicates conventional antibiotic therapy and drives demands for novel therapeutics. One promising novel approach is bacteriophage therapy, however this therapeutic has a narrow host range. Thus, understanding whether S. aureus FRIs are clonal or polyclonal is crucial for development of bacteriophage therapy. Consequently, the aim, of this study, was to evaluate 15 S. aureus clinical FRI isolates to determine clonality. For each individual FRI, eight colonies underwent whole-genome sequencing and results were compared to a reference strain to determine genomic variants. Isolates from each individual patient demonstrated greater than 92% shared genomic variants and over a 98% overlap with a merged variant profile, indicating clonal infections across all 15 FRIs. Furthermore, we assessed bacteriophage K activity to the planktonic states of the isolates for which there was similar activity against each individual FRI but different activity amongst the 15 FRI isolates. Lastly, we evaluated variations of genes associated with bacteriophage attachment receptors glycosylation (tarS, M, P) in which there were identical sequences across colonies for each individual FRI, indicating limited intra-infection variation in glycosylation potential of this receptor. This data supports that S. aureus FRI are clonal infections which typically have uniform bacteriophage attachment receptor glycosylation profiles within individual infections. These findings are vital for the development of bacteriophage therapy, suggesting that a single S. aureus colony is sufficient to conduct in vitro testing to determine bacteriophage activity to planktonic forms of S. aureus FRI in vivo. Yet further similar studies evaluating sessile heterogeneity are warranted. Nonetheless, the foundation of knowledge seen here supports further translational research and refinement of bacteriophage therapeutic strategies for S. aureus FRI.