Genotypic and phenotypic characterization of Staphylococcus epidermidis causing chronic relapsing prosthetic joint infections

Genotypic and phenotypic changes of Staphylococcus epidermidis during relapse episodes in prosthetic joint infections

Staphylococcus epidermidis is a coagulase-negative bacterium capable of causing recurrent relapses in prosthetic joint infection (PJI). The aim of this study was to determine if Staphylococcus epidermidis isolates from patients with recurrent relapses of prosthetic joint infection (PJI) changed genotypically (pulsed-field gel electrophoresis (PFGE) pattern analysis and genes involved in biofilm formation) and phenotypically (antimicrobial resistance, biofilm formation) during the different episodes. Four patients with PJI recurrent relapses were evaluated clinically and microbiologically. Genotypic and phenotypic characteristics of 31 S. epidermidis isolates were determined. In all cases, PJI was treated with antimicrobial therapy and resection of the prosthesis without reimplantation. Months later, all patients had a relapse episode and treated with rifampin plus vancomycin and surgical debridement. Changes in the antibiotics resistance profile in isolates from patients 1 and 2 were observed in the two episodes. Patient 1 had four clones A, B, C, and D that were distributed differentially in the two episodes. Similarly, patients 2 and 3 had two clones and subclones (E-E1 and F-F1, respectively), and patient 4 had only the clone G in both episodes. The clone F formed small-colony variants (SCVs). High level of biofilm formation was found in all clones, except for clones D and G. Clones/subclones showed a genotypic variation in icaA, sdrF, bap, sesI, and embp genes. The principal coordinate analysis showed that all clones/subclones were different. These results showed that the initial infective clone of S. epidermidis from PJI, changed genotypically and phenotypically after a second relapse as a response to the treatment.

Intraoperative Purulence Is Not Reliable for Diagnosing Periprosthetic Joint Infection

Purulence, defined as presence of pus, is based on subjective interpretation yet has been considered a definite sign of periprosthetic joint infection (PJI). 583 patients undergoing revision arthroplasty due to presumed PJI were retrospectively studied. PJI definition was independent of purulence, based on the definition of Musculoskeletal Infection Society recently modified by International Consensus Group on PJI. 498 patients fulfilled the criteria for definite PJI and 59 patients were deemed as aseptic. Purulence had sensitivity, specificity, positive and negative predictive values of 0.82, 0.32, 0.91, and 0.17, respectively. Purulence was not correlated with higher culture positivity yet was associated with higher synovial WBC counts (mean of 34.8 versus 5.2×10(3)/μL in patients without purulence [P<0.001]). In the absence of objective definition for purulence and in light of its inadequate test characteristics compared to a multi-criteria definition, purulence cannot serve as a single absolute diagnostic criterion for PJI.

LEVEL OF EVIDENCE

Level I, Diagnostic Studies.

Epidemiology and new developments in the diagnosis of prosthetic joint infection

Although prosthetic joint infection (PJI) is a rare event after arthroplasty, it represents a significant complication that is associated with high morbidity, need for complex treatment, and substantial healthcare costs. An accurate and rapid diagnosis of PJI is crucial for treatment success. Current diagnostic methods in PJI are insufficient with 10-30% false-negative cultures. Consequently, there is a need for research and development into new methods aimed at improving diagnostic accuracy and speed of detection. In this article, we review available conventional diagnostic methods for the diagnosis of PJI (laboratory markers, histopathology, synovial fluid and periprosthetic tissue cultures), new diagnostic methods (sonication of implants, specific and multiplex PCR, mass spectrometry) and innovative techniques under development (new laboratory markers, microcalorimetry, electrical method, reverse transcription [RT]-PCR, fluorescence in situ hybridization [FISH], biofilm microscopy, microarray identification, and serological tests). The results of highly sensitive diagnostic techniques with unknown specificity should be interpreted with caution. The organism identified by a new method may represent a real pathogen that was unrecognized by conventional diagnostic methods or contamination during specimen sampling, transportation, or processing. For accurate interpretation, additional studies are needed, which would evaluate the long-term outcome (usually >2 years) with or without antimicrobial treatment. It is expected that new rapid, accurate, and fully automatic diagnostic tests will be developed soon.