Whole-genome sequencing and in vitro characterization of a disseminated ST398 Staphylococcus aureus infection: A case report.

Staphylococcus aureus potentially causes systemic infections such as disseminated abscesses and bloodstream infections, leading to high mortality rates. We herein describe a case of disseminated muscle abscesses caused by sequence type (ST) 398 methicillin-sensitive S. aureus (MSSA), along with in vitro investigation results for potential pathogenic factors. A 67-year-old healthy woman was admitted to our hospital with complaints of systemic body pain. Blood cultures identified MSSA and contrast-enhanced computed tomography revealed multiple muscle abscesses extending from her neck to her soles. She received antibiotic treatment with intravenous cephazolin and underwent repeated surgical drainage, and was finally discharged. Notably, the MSSA strain exclusively affected her muscle tissues, prompting us to perform genetic analysis to uncover the underlying reason. Short-read genome analysis revealed the isolate to be ST398, harboring chp and scn genes known for immune evasion from human immunity. However, no other known pathogenic factors were identified despite rigorous assays for biofilm formation, surface and cell wall proteins, protease production, and hyaluronidase activity. ST398 S. aureus is commonly isolated from livestock, and her prior experience of being flooded could be related to the disease onset. The present case underscores the possibility of severe ST398 MSSA infections in humans, even in the absence of direct animal exposure.