# Pro-inflammatory secreted virulence factors of Staphylococcus capitis causing a rare occurrence of severe native hip joint infection

## TL;DR

A rare case of severe hip infection caused by Staphylococcus capitis is reported, with inflammation linked to specific secreted proteins.

## Contribution

Identification of two secreted virulence factors in S. capitis associated with a severe hip infection.

## Key findings

- S. capitis subspecies capitis was isolated from a severe hip infection with inflammatory destruction.
- The strain secreted a neutrophil pro-inflammatory autolysin protease and an analog of immunodominant antigen B.
- The infection was associated with the polysaccharide intercellular adhesin biofilm operon.

## Abstract

Staphylococcus capitis occasionally causes human infections. We report a case of S. capitis infection associated with inflammatory destructive hip abscess/osteomyelitis.

A 63-year-old man with severe hip osteoarthritis and recent left hip replacement presented with 2 months of worsening right hip pain. Radiographic imaging showed right femoral head destruction. The patient had no known hip trauma. His white blood cell count, C-reactive protein, and erythrocyte sedimentation rate were abnormal. Pre-operative aspirate of the hip showed purulent fluid. The examining radiologist believed the changes seen were due to inflammatory arthritis with infection from low-virulence organisms. The patient underwent image-guided biopsies of the synovium and the acetabulum, which showed pure cultures of S. capitis and infiltrating neutrophils. The patient’s native hip was removed, and an antibiotic spacer was placed. The patient was treated with intravenous cefazolin (6 weeks), after which he was transitioned to oral cefadroxil. The patient is doing well. The S. capitis was analyzed by nucleotide sequencing and biochemically for secreted virulence factors. The strain contained the polysaccharide intercellular adhesin biofilm operon. The strain was negative for urease, hemolysins, and major superantigens. The organism secreted a neutrophil pro-inflammatory autolysin protease and an analog of the immunodominant antigen B of S. aureus, previously with no known biological function.

Our data suggest that the inflammatory lesion in the patient’s right hip was due to S. capitis subspecies capitis, and furthermore, it is likely that two secreted proteins (autolysin and an analog of immunodominant antigen B) contributed to the inflammation.