Characterization of Staphylococcus Epidermidis isolates cultured from patients with infected hip prostheses

Background
Coagulase negative staphylococci are at the forefront of etiologic agents of periprosthetic joint infections (PJIs). The purpose of the study was to characterise causative isolates (n=19) of Staphylococcus epidermidis (SE) – with emphasis on their phenotypic and genotypic heterogeneity.

Material and methods
The isolates were cultured from multiple samples obtained perioperatively during revision surgery from 14 patients with clinically and/or microbiologically proven PJI. Phenotypic heterogeneity included variations of colony morphologies, drug resistance patterns and/or the capability of the biofilm formation and was verified by the DNA fingerprinting assay.

Results
Phenotypic discrepancies were observed between isolates cultured from 5 patients (35.7%). The genotyping assay identified 3 pairs of isolates as unrelated; single pairs were genetically related and indistinguishable. The biofilm production was detected in 17 isolates, among which 5 (29.4%) were proficient biofilm formers harbouring the icaADBC genes. Additionally, one ica-positive isolate produced a moderate, protease-sensitive biofilm. The remaining isolates were moderate biofilm producers among which four developed protease-sensitive biofilms.

Conclusions
The majority of PJIs are monoclonal; nevertheless, phenotypic diversity of SE is a frequent phenomenon which can complicate the diagnostic proceeding. Adherence ability is an important pathogenic trait of SE although the chemical composition of the resultant biofilm, its intensity and regulation of development can vary.