The role of Enterococcus faecalis in orthopaedic peri-implant infections demonstrated by automated ribotyping and cluster analysis

Enterococcus faecalis is an emerging etiologic agent of hospital infections, exhibiting high rates of antibiotic resistances. Here, 43 isolates of E. faecalis, taken from patients with implant orthopaedic infections come at the Rizzoli Orthopaedic Institute from 13 different Italian regions, were genotyped by an automated RiboPrinter and analyzed for antimicrobial susceptibility. The three most represented ribogroups were the iris-ribogroup, with its nine strains, the daisy-ribogroup, containing eight isolates, and the violet-ribogroup, with five isolates. The isolates belonging to the iris-ribogroup interestingly share a basal antibiotic resistance pattern, all being resistant to tetracycline, gentamicin and erythromycin. Among the isolates belonging to the daisy-ribogroup, 3 out of 8 were multi-resistant, 2 of which with the same pattern. More varied appeared the resistance profiles of the violet-ribogroup, in which 2 out of the five isolates were multi-resistant, the other being only bi- or mono-resistant. Noteworthy was also the variety of geographic origins and of implant infection sites for all the isolates. Cluster analysis demonstrated that ribogroups had a high internal similarity and that the three largest ones belonged to well-defined clusters, highlighting the tendency of E. faecalis to give rise to resistant clones in orthopaedic peri-implant infections.