Abstract
Well-organized ecosystems of bacteria colonize orthopaedic devices causing biofilm infections that are notoriously difficult to manage. Biofilms typically exhibit increased resistance to antibiotics leading to treatment failure, and tools for eradicating biofilms that do not increase antibiotic resistance are greatly needed. Antimicrobial photodynamic therapy (aPDT) is a promising form of treatment to combat clinically relevant biofilms. Exogenous provision of 5-aminolevulinic acid (5-ALA) to biofilm-forming clinical strains of E.coli, E. faecalis and S. aureus was recently shown by several research groups to result in the accumulation of sufficient quantities of endogenous photosensitizers porphyrins (protoporphyrin IX, coproporphyrin III and others), via the heme biosynthetic pathway, to produce a significant phototoxic effect when exposed to activating light. For clinical translation of this extremely promising approach, here we develop a portable light source for 5-ALA-based aPDT of orthopaedic implant biofilms, spectrally shaped for optimal porphyrin light absorption at wavelengths range approved by FDA for clinical use. After phantom calibration, we tested it on E.coli-E.faecalis biofilms grown in soft lithography-fabricated microfluidic chips and on methicillin-resistant S. aureus (MRSA) biofilms grown on titanium and stainless steel orthopaedic hardware in custom-designed macrofluidic devices. Successful in-vitro experiments allowed us to conduct a proof-of-concept validation study in a preclinical rat model of MRSA-contaminated open fracture. Following tibia fracture and two hours of wound infection development, a one hour incubation with 20% 5-ALA and treatment with either 90J/cm(2) or three fractions of 30J/cm(2) light doses demonstrated 94% and 99% overall reduction of MRSA, respectively, while the temperature of the tissue remained <39°C, below the threshold for thermal damage. The encouraging results suggest further preclinical testing of the developed light source for optimization of aPDT regimen and 5-ALA concentration to reduce the risk of long-term side effects in animal models of contaminated trauma surgery.