[Peptostreptococcus magnus osteoarticular infections after orthopedic surgery. 14 cases and pathogenicity factors]

We report a retrospective study of 14 Peptostreptococcus magnus bone and joint infections, following orthopaedic prostheses or implantation of fixation devices, diagnosed in two Paris hospitals between 1992 and 1996. Five patients experienced a knee joint infection after anterior cruciate ligament reconstruction with 4 artificial grafts, and 9 caught joint or wound infections, after limb traumatic injuries or bone neoplastic ruptures involving femur, tibia, calcaneum and humerus, treated by arthroplasty or osteosynthesis with implantation of biomaterials. Septic arthritis was experienced one week to one year after reconstructive surgery, and had evolved for several months to years before etiologic diagnosis in 5 cases. Specimens of pus, tissues or removed implants produced numerous slow growing small colonies of Gram positive cocci arranged in clumps on culture media incubated in anaerobic atmosphere only. In 10 patients, the same organism was disclosed in several separate specimens. The identification of P. magnus was assessed by the enzyme profile (rapid ID 32A API strips), gaz liquid chromatography, catalase and coagulase production, resistance to novobiocin and Na polyanethol sulphonate. Antibiotic sensitivity testing performed by disc method was constant to penicillin G, amoxicillin, cefuroxime, cefoxitin, imipenem and pristinamycin with penicillin G MICs < 0.125 mg/l and metronidazole MICs < 1 mg/l. Erythromycin, clindamycin, rifampicin, tetracycline and fosfomycin were active against more than 70% of P. magnus. All patients were cured after a prolonged course of various antibiotics and surgical removal of the foreign material whenever possible. We studied in vitro binding of P. magnus with extracellular matrix proteins adsorbed onto biomaterials, by particle agglutination assays of latex beads coated with proteins. Eighty one% of strains bound to collagen, 69% to fibrinogen and 46% to fibronectin. Comparison of orthopaedic strains with strains of other infections and from skin showed a correlation between P. magnus from bone and joint infections and their fibrinogen binding ability (69% against 20%, p < 0.05).