The World Health Organization has been alerting that the “post-antibiotic era” is approaching, making the search for alternative antimicrobial therapies mandatory. Antimicrobial photodynamic therapy (aPDT) has been gaining prominence due to its non-specific mechanism of action, which relies on the generation of reactive oxygen species upon the activation of a photosensitizer (PS) by light of a specific wavelength in the presence of oxygen. However, the discussion of whether or not aPDT can induce bacterial resistance is controversial. In that sense, the aim of this study was to determine if multiple cycles of suboptimal doses of aPDT could induce resistance in Enterococcus faecalis. First, we determined optimal and suboptimal conditions of aPDT employing chlorin-e6 (Ce6) and methylene (MB) for planktonic E. faecalis. The combinations of light dose and PS concentration that induced bacterial reductions between 1 log10 and 3 log10 of CFU/mL were selected to start the cycles (21 µM of Ce6 + 45 J/cm²; and 78 µM of MB + 80 J/cm²). The cycling consisted of treatment, plating on PS-free blood agar and recovering grown colonies to start again. By the end of four cycles, cells treated with both Ce6-aPDT or MB-aPDT were completely eliminated, after sustaining a stable survival rate through the first three cycles. We employed two different PS and observed the same outcomes for both of them, indicating the results were not PS-dependent. Our findings are of paramount importance since they are in the way to prove that bacterial resistance cannot be induced by this approach.
Laura M. de Freitas, Ana L. Blanco, and Carla R. Fontana, "Antimicrobial photodynamic therapy proved not to induce bacterial resistance (Conference Presentation)," Proc. SPIE 10479, Light-Based Diagnosis and Treatment of Infectious Diseases, 1047919 (Presented at SPIE BiOS: January 31, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2287268.5751486414001.
Conference Presentations are recordings of oral presentations given at SPIE conferences and published as part of the conference proceedings. They include the speaker's narration along with a video recording of the presentation slides and animations. Many conference presentations also include full-text papers. Search and browse our growing collection of more than 12,000 conference presentations, including many plenary and keynote presentations.