# Polymicrobial Late-Onset Knee Prosthetic Joint Infection Involving Parvimonas micra: A Case Report and Genomic Characterization

## TL;DR

A rare case of knee prosthetic joint infection involving Parvimonas micra and Staphylococcus aureus is reported, with genomic insights into the pathogen's virulence and treatment outcomes.

## Contribution

This case highlights the overlooked role of Parvimonas micra in chronic prosthetic joint infections and provides genomic characterization of its virulence traits.

## Key findings

- The P. micra strain showed 97.2% identity to a reference strain and carried virulence genes like groEL, tufA, clpP, and gaIE.
- Resistance genes vanW, vanT, and vanY were detected, but vanA and vanB were absent.
- The patient's symptoms resolved after two-stage revision surgery and targeted antimicrobial therapy.

## Abstract

We report a rare case of polymicrobial late-onset knee prosthetic joint infection (PJI) caused by Parvimonas micra and Staphylococcus aureus. An 80-year-old woman with multiple comorbidities presented, five years after total knee arthroplasty, with progressive pain and radiographic signs of prosthetic loosening. Synovial fluid analysis revealed marked neutrophilic inflammation, and intraoperative tissue cultures, including sonication fluid yielded both pathogens. Identification was confirmed by MALDI-TOF MS and whole-genome sequencing (WGS). The P. micra strain showed 97.2% identity to reference strain SAMN29629855, and carried virulence genes such as groEL, tufA, clpP, ctrD, srtC4, and gaIE, associated with oxidative stress response, adhesion, immune evasion, and biofilm formation. Resistance genes vanW, vanT, and vanY from the van operon were also detected, though vanA and vanB were absent. The patient underwent a two-stage revision surgery and a 12-week course of pathogen-targeted antimicrobial therapy, with complete resolution of symptoms and no recurrence after 12 months. This case highlights the overlooked pathogenicity of P. micra in chronic PJIs, especially in polymicrobial biofilm-related infections. The integration of WGS provided valuable insights into possible genetic characteristics of virulence determinants of this rare cause of PJI.