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Published on: December 3, 2017
Heterogeneity of Staphylococcus epidermidis in prosthetic joint infections: time to reevaluate microbiological
Micael Widerström1, Marc Stegger2, Anders Johansson3
1Department of Clinical Microbiology, Umeå University, SE-901 85, Umeå, Sweden. micael.widerstrom@umu.se.
Abstract:
Prosthetic joint infection (PJI) is a feared and challenging to diagnose complication after arthroplasty, with Staphylococcus epidermidis as the major pathogen. One important criteria to define PJI is the detection of phenotypically indistinguishable microorganisms with identical antibiotic susceptibility pattern in at least two different samples. However, owing to phenotypical variation within genetic clones and clonal variation within a phenotype, the criteria may be ambiguous. We investigated the extent of diversity among coagulase-negative staphylococci (CoNS) in PJI and characterised S. epidermidis isolates from PJI samples, specifically multiple S. epidermidis isolates identified in individual PJI patients. We performed a retrospective cohort study on 62 consecutive patients with PJI caused by CoNS from two hospitals in Northern Sweden. In 16/62 (26%) PJIs, multiple S. epidermidis isolates were available for whole-genome analyses. Hospital-adapted multidrug-resistant genetic clones of S. epidermidis were identified in samples from 40/62 (65%) of the patients using a combination of pulsed-field gel electrophoresis and multilocus sequence typing. Whole-genome sequencing showed the presence of multiple sequence types (STs) in 7/16 (44%) PJIs where multiple S. epidermidis isolates were available. Within-patient phenotypical variation in the antibiotic susceptibility and/or whole-genome antibiotic resistance gene content was frequent (11/16, 69%) among isolates with the same ST. The results highlight the ambiguity of S. epidermidis phenotypic characterisation as a diagnostic method in PJI and call for larger systematic studies for determining the frequency of CoNS diversity in PJIs, the implications of such diversity for microbiological diagnostics, and the therapeutic outcomes in patients.
Insights
Prosthetic joint infections (PJIs) caused by Staphylococcus epidermidis show significant genetic diversity within patients. This diversity challenges current diagnostic criteria, impacting treatment strategies for these difficult infections.
Area of Science:
- Microbiology
- Infectious Diseases
- Genomics
Background:
- Prosthetic joint infection (PJI) is a serious complication of arthroplasty.
- Staphylococcus epidermidis is the primary pathogen in PJIs.
- Current diagnostic criteria for PJI rely on phenotypic similarity of microorganisms across samples, which can be ambiguous.
Purpose of the Study:
- To investigate the genetic diversity of coagulase-negative staphylococci (CoNS), particularly Staphylococcus epidermidis, in PJI.
- To evaluate the diagnostic ambiguity arising from phenotypic variation within genetically similar isolates.
- To assess the prevalence of hospital-adapted multidrug-resistant S. epidermidis clones in PJI.
Main Methods:
- Retrospective cohort study of 62 patients with CoNS- PJI.
- Whole-genome sequencing, pulsed-field gel electrophoresis, and multilocus sequence typing were used.
- Analysis of multiple S. epidermidis isolates from individual PJI patients.
Main Results:
- Multiple sequence types (STs) of S. epidermidis were found in 44% of PJIs with multiple isolates.
- Within-patient phenotypic variation in antibiotic susceptibility and resistance genes was common (69%) among isolates with the same ST.
- Hospital-adapted multidrug-resistant S. epidermidis clones were identified in 65% of patients.
Conclusions:
- Phenotypic characterization of S. epidermidis in PJI can be ambiguous due to significant within-patient genetic and phenotypic diversity.
- Further research is needed to understand the implications of CoNS diversity for microbiological diagnostics and therapeutic outcomes in PJI.
- Genomic analysis offers a more precise approach to characterizing S. epidermidis in PJI.
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