Clinical Utilization of Species-Specific Immunoassays for Identification of S. aureus and Streptococcus agalactiae in Orthopaedic Infections.

Staphylococcus aureus and Streptococcus agalactiae (Group B Streptococcus, GBS) are common causes of deep musculoskeletal infections (MSKI) and result in significant patient morbidity and cost to the healthcare system. One of the major challenges with MSKI is the lack of faithful diagnostics to correctly identify the primary pathogen, as standard culture based assays are prone to false positives in the case of polymicrobial infections, and false negatives due to limitations in sample acquisition and antibiotic use prior to presentation. To improve upon our current diagnostic methods for MSKI, we developed a multiplex immunoassay for antigen specific IgGs in serum (Luminex), and medium enriched for newly synthesized antibodies (MENSA) for anti-S. aureus and GBS generated from cultured peripheral blood mononuclear cells (PBMCs) of orthopaedic infection patients undergoing surgical treatment. Samples were obtained from 110 MSKI patients: 80 diabetic foot ulcer, 21 periprosthetic joint infection, 5 septic arthritis, 2 spine, 1 hand, and 1 fracture related infection (FRI). Anti-S. aureus and anti-GBS antibody titers were compared to culture results to assess their concordance in identifying the pathogens. Immunoassay, particularly MENSA, showed high diagnostic potential for monomicrobial S. aureus and GBS orthopaedic infections (AUC > 0.95). MENSA also demonstrated diagnostic potential for GBS polymicrobial orthopaedic infection and for GBS DFU (AUC > 0.83 for both). Serum showed high diagnostic potential for S. aureus PJI (AUC > 0.95). Taken together, these findings support the development of species-specific immunoassays for the identification of causal pathogens in active MSKI, especially in conjunction with standard culture. This article is protected by copyright. All rights reserved.