Peptostreptococcus magnus does not cause hematogenous infections in experimental arthroplasties

Rabbits with cemented endoprostheses in the knee joints were given 1-ml intravenous injections of suspensions containing Peptostreptococcus magnus (3 x 10(8) colony-forming units/ml) on three consecutive days seven weeks postoperatively. The animals were killed after another seven weeks. The bacterial challenge did not result in infection. This is in contrast to a previous study using the same experimental system with another anaerobic bacterial species, Propionibacterium acnes, which caused infection in approximately 50% of the animals. Both these bacteria have previously been reported to cause late infections in human arthroplasties. The present results may indicate differences in the spreading mechanisms, i.e., that Peptostreptococcus magnus may have a limited ability to cause hematogenic infections and that late infections of endoprostheses by Peptostreptococcus magnus are due to perioperative contamination.