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Hemolysis as a clinical marker for propionibacterium acnes orthopedic infection
Scott R Nodzo1, Donald W Hohman, John K Crane
1Department of Orthopaedics, State University of New York, Buffalo, NY. spodzo@gmail.com.
Abstract:
Determining if a Propionibacterium acnes culture is a true infection or a contaminant remains a challenge. We conducted a study to distinguish between a true infection and a contaminated culture based on the P acnes hemolytic phenotype and clinical presentation. All P acnes strains were from orthopedic patients who had undergone arthroplasty or nonarthroplasty shoulder procedures. Hemolysis was determined according to P acnes growth on brucella blood agar plates after 48 to 72 hours. Each patient record that corresponded to the obtained P acnes strains was retrospectively reviewed for clinical data. An orthopedic surgeon involved in the care of the patients, but blinded to the hemolytic status of the bacteria, classified these infections as definite, likely, or unlikely. Of the 22 P acnes strains, 13 were hemolytic, and 9 were nonhemolytic. Of the 13 hemolytic strains, 10 were definite infections; only 3 of the 9 nonhemolytic strains were definite infections. Mean (SD) C-reactive protein level was significantly higher (P = .03) in the hemolytic group, 16 (11) mg/mL, than in the nonhemolytic group, 7.9 (10) mg/mL. A hemolytic phenotype of P acnes may represent a more pathogenic strain of bacteria, and may be more likely to be found in patients with a definite infection with P acnes rather than a contaminated culture.
Insights
A hemolytic phenotype in Propionibacterium acnes (P. acnes) may indicate a true orthopedic infection rather than a contaminant. This finding helps differentiate pathogenic P. acnes strains in patients.
Area of Science:
- Orthopedics
- Infectious Diseases
- Microbiology
Background:
- Distinguishing true Propionibacterium acnes infections from contaminants is clinically challenging.
- P. acnes is associated with orthopedic device-related infections and native joint infections.
Purpose of the Study:
- To determine if the hemolytic phenotype of P. acnes correlates with true infection in orthopedic patients.
- To investigate the association between P. acnes hemolysis and clinical presentation.
Main Methods:
- Retrospective review of orthopedic patient records with P. acnes isolates.
- Assessment of P. acnes hemolytic phenotype on brucella blood agar.
- Classification of infection status by a blinded orthopedic surgeon.
- Comparison of C-reactive protein levels between hemolytic and nonhemolytic groups.
Main Results:
- Of 22 P. acnes strains, 13 were hemolytic and 9 nonhemolytic.
- Hemolytic P. acnes strains were more frequently associated with definite infections (10/13) compared to nonhemolytic strains (3/9).
- Mean C-reactive protein levels were significantly higher in patients with hemolytic P. acnes (16 mg/mL) than nonhemolytic P. acnes (7.9 mg/mL).
Conclusions:
- A hemolytic P. acnes phenotype may indicate a more pathogenic bacterial strain.
- The hemolytic phenotype is a potential marker for differentiating true P. acnes infections from contaminated cultures in orthopedic settings.
