Septic nonunions of lower limb long bones: don't neglect Propionibacterium acnes!

We report 3 clinical cases of septic nonunions of lower limb long bones in which the pathogenicity of Propionibacterium acnes was retained after several weeks of poor outcome. The patients had fractures that were treated by internal fixation, without initially suspected infection. The diagnosis of delayed union coincided with the onset of treatment. Support was performed in 2 steps, allowing for the collection of several deep samples that were referred for microbiological analysis. Molecular techniques for microbiological investigation were performed on perioperative samples and were not contributive. The detection of P acnes, which was identified after several days of incubation, prompted us to consider the role of this bacterium. The presence of P acnes is regularly interpreted as contamination of samples during collection or handling in the laboratory. A multidisciplinary decision to make the diagnosis of surgical site infection with P acnes and specific antibiotic treatment for several months led to consolidation in all the patients. The ability of bacteria of the genus Propionibacterium to cause insidious surgical site infections should not be underestimated, and more extensive sample incubation is essential to diagnose such infections.