Inhibition of fracture healing in the presence of contamination by Staphylococcus aureus: Effects of growth state and immune response

Extremity injuries comprise a significant portion of trauma, affecting quality of life, financial burden, and return to duty. Bacterial contamination is commonly associated with failure to heal, despite antibiotic treatment, suggesting that additional therapies must be developed to combat these complications. Treatment failure is likely due to the presence of resistant microbial communities known as biofilms. Biofilm bacteria are able to elicit a direct inhibition of healing through a multitude of known factors. However, they likely also inhibit healing through alteration of the inflammatory response. As inflammation is a critical step in fracture healing, how the presence of biofilm bacteria shifts this response to one that is suboptimal for healing is an important consideration that is currently understudied. The profile of inflammatory factors in response to biofilm bacteria is unique and distinct from those induced during normal healing or by planktonic bacteria alone. This review will examine the presence of inflammatory factors during normal healing and those induced by contaminating bacteria, and will discuss how these differences may ultimately lead to nonunion. Specifically, this review will focus on the Th1/Th2/Th17 type inflammatory responses and how shifts in the balance of these responses during infection can lead to both ineffective clearance and disruption of fracture healing.