Aim

Cutibacterium acnes is a major skin commensal that may also act as an opportunistic pathogen. Findings of C. acnes in tissue cultures obtained during arthroplasty revision surgery are difficult to interpret, since they may represent true infection or contamination. This study investigated whether C. acnes isolates obtained from prosthetic joint infections (PJIs) were related and shared common genomic traits that might correlate with clinical courses and patient outcomes.

Implementation of new diagnostic methods (i.e. MALDI-TOF MS) has made it possible to identify coagulase-negative staphylococci (CoNS) to species level in routine practice. Further knowledge about clinical and microbiological characteristics of prosthetic joint infections (PJIs) caused by different CoNS may both facilitate interpretation of microbiological findings and improve clinical algorithms.

The aim of this study was clinical and microbiological characterization of PJIs caused by Staphylococcus capitis.

Patients with PJIs caused by S. capitis (growth in ≥2 perioperative tissue samples, n=19, identified by MALDI-TOF MS) from three centres between 2005–2014 were included. Medical records were examined (n=16). Further characterization of S. capitis was performed; rep-PCR (Diversilab, BioMerieux), standard antibiotic susceptibility testing, GRD Etest and macromethod Etest for detection of heteroresistant subpopulations and microtitre plate assay for detection of biofilm production.

Multi-drug resistant (MDR) S. capitis (R≥3 antibiotic groups) was detected in 5/19(26%) of isolates, 1/19(5%) were ciprofloxacin resistant and no isolates was rifampin resistant. Biofilm formation was present in 14/19(74%). The dendrograms created by rep-PCR showed two distinct clusters, including one that contained isolates from all centres, as well as the reference isolates. Furthermore, three additional clusters were identified, all of these mainly obtained from single centres. In two of these, MDR was highly prevalent. In one of these clusters, 4 of the 8 strictly monomicrobial infections were found.

All of the PJIs were defined as either early postinterventional (10/16) or chronic (6/16). No late haematogenous infection was found. The highest CRP values were reported in monomicrobial infections. Wound healing disturbances was noted in 8/10 early postinterventional infections. Fever was absent in chronic infections, sinus tracts rare (1/6), while pain was a common symptom (5/6).

S. capitis has the potential to cause PJIs, both by itself as well as part of a polymicrobial infection. The antibiotic susceptibility patterns were more favourable than has previously been reported in S. epidermidis isolated from PJIs(1). Clinical data suggests that PJIs caused by S. capitis were acquired perioperatively or in the early postoperative phase. The clustering found by rep-PCR together with data showing high prevalence of S. capitis in the air of operation rooms during prosthetic joint surgery(2) implicates that nosocomial spread might be present. Epidemiological surveillance may be of value in order to ensure early detection of nosocomial transmission.

Grants were received from the research committees of Värmland County Council and Örebro University, Sweden.