MnTE-2-PyP disrupts Staphylococcus aureus biofilms in a novel fracture model

Biofilm-associated infections in orthopedic surgery lead to worse clinical outcomes and greater morbidity and mortality. The scope of the problem encompasses infected total joints, internally fixed fractures, and implanted devices. Diagnosis is difficult. Cultures are often negative, and antibiotic treatments are ineffective. The infections resist killing by the immune system and antibiotics. The organized matrix structure of extracellular polymeric substances within the biofilm shields and protects the bacteria from identification and immune cell action. Bacteria in biofilms actively modulate their redox environment and can enhance the matrix structure by creating an oxidizing environment. We postulated that a potent redox-active metalloporphyrin MnTE-2-PyP (chemical name: manganese (II) meso-tetrakis-(N-methylpyridinium-2-yl) porphyrin) that scavenges reactive species and modulates the redox state to a reduced state, would improve the effect of antibiotic treatment for a biofilm-associated infection. An infected fracture model with a midshaft femoral osteotomy was created in C57B6 mice, internally fixed with an intramedullary 23-gauge needle and seeded with a biofilm-forming variant of Staphylococcus aureus. Animals were divided into three treatment groups: control, antibiotic alone, and combined antibioticplus MnTE-2-PyP. The combined treatment group had significantly decreased bacterial counts in harvested bone, compared with antibiotic alone. In vitro crystal violet assay of biofilm structure and corresponding nitroblue tetrazolium assay for reactive oxygen species (ROS) demonstrated that MnTE-2-PyP decreased the biofilm structure and reduced ROS in a correlated and dose-dependent manner. The biofilm structure is redox-sensitive in S. aureus and an ROS scavenger improved the effect of antibiotic therapy in model of biofilm-associated infections.