Propionibacterium acnes: An agent of prosthetic joint infection and colonization

Summary

Background

Prosthetic joint infection (PJI) can present a diagnostic challenge, especially with slow-growing and poorly virulent bacteria.

Objective

To describe the epidemiological, clinical and biological characteristics of Propionibacterium acnes PJI, their treatments and outcomes and compare 2 clinical pictures (according to the time PJI symptoms appeared after the index operation: ≤2 years, >2 years).

Methods

We conducted a cohort study on P. acnes PJI. Diagnosis was based on ≥2 positive cultures of intraoperative specimens taken during revision arthroplasties for infection or presumed aseptic loosening.

Results

Fifty patients with prosthetic hip (34), knee (10) or shoulder (6) infections were included and analyzed according to their symptom-free interval: ≤2 years for 35 and >2 years for 15 (mean interval: 11 ± 6 years). The numbers of previous prostheses (p = 0.04) were higher for the shorter-interval group, which had more frequent signs of infection (p = 0.004). These findings suggest infection in most of the patients whose PJI symptoms appeared: ≤2 years after the index operation, and colonization in the majority of those whose symptoms appeared >2 years after index surgery. Treatment combining exchange arthroplasty with prolonged intravenous antibiotics was successful for 92% of the patients.

Conclusion

P. acnes can cause different types of PJI: late chronic infections, colonization of loosened prostheses and, exceptionally, acute postoperative infections.

Introduction

Propionibacterium acnes (P. acnes) is a nonspore-forming anaerobic bacillus. This commensal bacterium of the deep layers of skin, respiratory, digestive and eye mucosa1, 2 has low level virulence, but its pathogenic role is now clearly established in a variety of infections: endocarditis,3, 4 meningitis and brain abscess,5, 6 endophthalmitis and conjunctivitis,⁷ arthritis,⁸ osteomyelitis⁹ and spondylitis.10, 11, 12 Major predisposing conditions are previous surgery and implantation of foreign bodies, such as prosthetic heart valves, ventriculoperitoneal shunts, intraocular lenses, orthopedic implants and joint prostheses.1, 2, 6, 9, 13, 14, 15, 16, 17, 18, 19 Clinical presentation is usually insidious. Acute P. acnes infections (sepsis, meningitis, spinal osteomyelitis, …) are very unusual.20, 21, 22 Reports on P. acnes prosthetic joint infection (PJI) are rare.9, 16, 17, 18, 19 Detailed characteristics of these poorly known infections have been described in only a few case reports9, 18, 19 and data on long-term outcome are generally unavailable.

The number of P. acnes PJI is certainly underestimated. Indeed, diagnosis may be difficult in patients with no fever or local inflammation and normal blood tests, and this pathogen is often considered a contaminant, or not isolated at all, because of its slow growth that requires at least 5 days of culture on standard agar plates and sometimes up to 15 days in enriched broth.

We report on 50 cases of P. acnes PJI and describe the epidemiological, clinical and biological characteristics of these infections, their treatments and long-term outcomes. We separated patients into 2 groups according to the time until PJI symptoms appeared after the index operation (≤2 years, >2 years) and compared their characteristics. We choose 2 years, as most of PJI infections acquired during prosthesis implantation develop within that period.²³