Methicillin-resistant Staphylococcus epidermidis in the nasal and skin microbiota of patients planned for prosthetic joint surgery

Staphylococcus epidermidis, ubiquitous in the human nare and skin microbiota, is a common causative microorganism in prosthetic joint infections (PJIs). A high proportion of PJI isolates have been shown to harbour genetic traits associated with resistance to/tolerance of agents used for antimicrobial prophylaxis in joint arthroplasties. These traits were found within multidrug resistant S. epidermidis (MDRSE) lineages of multiple genetic backgrounds. In this study, the aim was to study whether MDRSE lineages previously associated with PJIs were present, before hospitalization, in the nasal and skin microbiota of patients scheduled for arthroplasty. Using agar plates selective for methicillin resistance, we cultured samples from the nares, inguinal crease, and skin over hip/ knee (depending on the planned procedure) of 66 patients taken two weeks (median) before admission to hospital for total joint arthroplasty. S. epidermidis colonies were identified and tested for mecA. Methicillin-resistant S. epidermidis (MRSE) were characterized by Illumina-based whole-genome sequencing. Using this method, we found that 30/66 (45%) of patients were colonized with MRSE at 1-3 body sites. A subset of patients, 10/66 (15%), were colonized with MDRSE lineages associated with PJIs in Sweden. The qacA gene, associated with tolerance of chlorhexidine, was identified in MRSE isolates from 19 out of 30 (63%) of MRSE colonized patients, whereas genes associated with aminoglycoside resistance were less common, found in 11/30 (37%). We found that MDRSE lineages previously associated with PJIs are present in a subset of patients' pre-admission microbiota, plausibly in low relative abundance, and may be selected for by the current prophylaxis regimen comprising whole-body cleansing with chlorhexidine-gluconate containing soap. To further lower the rate of S. epidermidis PJIs current prophylaxis may need to be modified, but it is important that possible perioperative MDRSE transmission events and specific risk factors for MDRSE PJIs be investigated before revaluating antimicrobrial prophylaxis.