Motivation for the study
Periprosthetic joint infections after hip and knee replacement surgeries are associated with high patient morbidity and a large financial cost. Challenging two-stage revision surgeries are required with long antibiotics regimes that can have limited efficacy and cannot eradicate drug-resistant strains like MRSA (methicillin-resistant Staphylococcus aureus). This study aims to investigate the potential of photodynamic therapy with methylene blue to eradicate problematic bacteria associated with joint infections.
To determine the effectiveness of methylene blue PDT it is important to understand the effect of both drug and light dose on treatment response. The effectiveness of different methylene blue concentrations on MRSA bacterial growth inhibition was first studied on Petri dishes with or without laser light (ML7000 series laser system, 665 nm, 35 mW/cm2, 16 min irradiation). Different laser doses (15, 25, 30, 35, 40 and 45 J/cm2) were also studied with constant methylene blue concentration (0.3 mM) to understand how increasing light dose affects the treatment response. Plates were incubated at 37 ⁰C and visually inspected the next day.
Optimal methylene blue concentration against MRSA
Methylene blue alone had little effect against MRSA: while increasing the concentration of methylene blue has some effect, a significant number of colonies are left even at the highest concentration studied. When combined with laser activation, MRSA colonies are effectively eradicated at all studied concentrations of methylene blue.
Optimal laser dose for antimicrobial PDT
Increasing the laser power improved the efficacy of antimicrobial PDT. Control plates where no laser was applied had no effect on bacterial growth, while laser doses of 15 J/cm2 and 30 J/cm2 were effective but a few resistant colonies were left. Laser light dose of 35 J/cm2 was the lowest laser dose that eradicated all bacteria.
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Antimicrobial photodynamic therapy–a promising treatment for prosthetic joint infections
Timothy Briggs, Gordon Blunn, Simon Hislop, Rita Ramalhete, Caroline Bagley, David McKenna, Melanie Coathup
Lasers Med Sci, 2018, 33 (3)
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