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Staphylococcus epidermidis is the most important pathogen in infections related to implanted foreign materials, especially prosthetic joint infections (PJIs). The aim of this study was to investigate the antimicrobial activities of 16 antibiotics against S. epidermidis isolated from PJIs, with special focus on rifampicin and rpoB variability. Ninety-one per cent of the isolates were multiresistant (i.e. resistant to members of more than three classes of antibiotics). Thirty-nine per cent were resistant to rifampicin, associated with one or two single-nucleotide polymorphisms (SNPs) in rpoB. Using IsoSensitest agar with supplements, 61% were resistant to oxacillin, and using Mueller-Hinton II agar with supplement, 84% were resistant. Using the Etest, 58% were resistant to cefoxitin, and using the disk diffusion test, 91% were resistant. The mecA gene was detected in 85% of the isolates. Regarding recently available antibiotics, all isolates were susceptible to tigecycline and linezolid, and 97% were susceptible to daptomycin. In addition, two novel antibiotics, dalbavancin and ceftobiprole, were tested, although not yet available for routine use. The MIC(50) and MIC(90) values of these novel antibiotics were 0.032 and 0.047 mg/L and 0.5 and 1.5 mg/L, respectively. Among the other antibiotics, the rates of resistance varied between 0% (vancomycin) and 82% (trimethoprim-sulphamethoxazole). S. epidermidis strains causing PJIs often show multiresistance, including resistance to rifampicin, which is mainly caused by one or two SNPs. Some of the newer antimicrobial agents may provide alternatives for monotherapy or combination therapy with rifampicin. Detection of mecA is necessary before initiating treatment of infections due to S. epidermidis when it displays intermediate susceptibility to cefoxitin.

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Further knowledge about the clinical and microbiological characteristics of prosthetic joint infections (PJIs) caused by different coagulase-negative staphylococci (CoNS) may facilitate interpretation of microbiological findings and improve treatment algorithms. Staphylococcus capitis is a CoNS with documented potential for both human disease and nosocomial spread. As data on orthopaedic infections are scarce, our aim was to describe the clinical and microbiological characteristics of PJIs caused by S. capitis. This retrospective cohort study included three centres and 21 patients with significant growth of S. capitis during revision surgery for PJI between 2005 and 2014. Clinical data were extracted and further microbiological characterisation of the S. capitis isolates was performed. Multidrug-resistant (≥3 antibiotic groups) S. capitis was detected in 28.6 % of isolates, methicillin resistance in 38.1 % and fluoroquinolone resistance in 14.3 %; no isolates were rifampin-resistant. Heterogeneous glycopeptide-intermediate resistance was detected in 38.1 %. Biofilm-forming ability was common. All episodes were either early post-interventional or chronic, and there were no haematogenous infections. Ten patients experienced monomicrobial infections. Among patients available for evaluation, 86 % of chronic infections and 70 % of early post-interventional infections achieved clinical cure; 90 % of monomicrobial infections remained infection-free. Genetic fingerprinting with repetitive sequence-based polymerase chain reaction (rep-PCR; DiversiLab®) displayed clustering of isolates, suggesting that nosocomial spread might be present. Staphylococcus capitis has the potential to cause PJIs, with infection most likely being contracted during surgery or in the early postoperative period. As S. capitis might be an emerging nosocomial pathogen, surveillance of the prevalence of PJIs caused by S. capitis could be recommended.