Cutibacterium is recognized as the most common organism recovered from failed shoulder joint replacements. Shoulder arthroplasty wounds are often inoculated by Cutibacterium released from the dermal pilocebaceous units when the skin is incised. When these planktonic (free floating) bacteria come in contact with prosthetic joint surfaces, they can form a biofilm that protects them from antibiotics and host defenses. Efforts to minimize the risk of periprosthetic infections focus on minimizing the size of the inoculum and on killing the introduced organisms before they have an opportunity to form a durable biofilm.

Here are a few relevant articles

Biofilm formation by Propionibacterium acnes is a characteristic of invasive isolates

Propionibacterium acnes (Cutibacterium) has been shown to form biofilm both in vitro and

in vivo. These authors analyzed biofilm formation by 93 P. acnes isolates, either from invasive infections (n = 45) or from the skin of healthy people (n = 48). The majority of isolates from deep infections produced biofilm in a microtitre model of biofilm formation, whereas the skin isolates were poor biofilm producers (p <0.001 for a difference). They concluded that there was a role for biofilm formation in P. acnes virulence. The type distribution, as determined by sequencing of recA, was similar among isolates isolated from skin and from deep infections, demonstrating that P. acnes isolates with different genetic backgrounds have pathogenic potential. The biofilm formed on plastic and on bone cement was analysed by scanning electron microscopy (EM) and by transmission EM. The biofilm was seen as a 10-lm-thick layer covering the bacteria and was composed of filamentous as well as more amorphous structures. Interestingly, the presence of human plasma in solution or at the plastic surface inhibits biofilm formation, which could explain why P. acnes primarily infect plasma-poor environments

of, for example, joint prostheses and cerebrospinal shunts. This work underlines the importance of biofilm formation in P. acnes pathogenesis, and shows that biofilm formation should be considered in the diagnosis and treatment of invasive P. acnes infections.

Delayed Propionibacterium acnes surgical site infections occur only in the presence of an implant

These authors used a mouse model to compare the effects of P. acnes inoculation with an implant into the mouse femur to a control group with the bacteria but no implant. They observed the animals over a 6-month period using optical imaging system. During the first 2 weeks, bacterial signals were detected in the femur in the both groups. The bacterial signal completely disappeared in the control group within 28 days. Interestingly, in the implant group, bacterial signals were still present 6 months after inoculation. Histological and scanning electron-microscope analyses confirmed that P. acnes was absent from the control group 6 months after inoculation, but in the implant group, the bacteria had survived in a biofilm around the implant. PCR analysis also identified P. acnes in the purulent effusion from the infected femurs in the implant group.

A Comparison of Bacterial Adhesion and Biofilm Formation on Commonly Used Orthopaedic Metal Implant Materials: An In vitro Study

These authors conducted an in vitro study is to evaluate the ability of Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa to adhere to and to form biofilms on the surface of five orthopaedic biomaterials: cobalt and chromium, highly cross-linked polyethylene, stainless steel, trabecular metal, and titanium alloy. While Cutibacterium was not included, they did include the second most common infecting organism for shoulder periprosthetic infections, S. epidermidis. They found that the highest level of adherence was observed on highly cross-linked polyethylene, followed by titanium, stainless steel, and trabecular metal, with the lowest occurring on the cobalt-chromium alloy. Among the bacterial strains tested, the ability for high adherence was observed with S. epidermidis and K. pneumoniaefollowed by P. aeruginosa and E. coli, whereas S. aureus showed the least adherence.