In vitro photodynamic inactivation effects of cationic benzylidene cyclopentanone photosensitizers on clinical fluconazole-resistant Candida albicans planktonic cells and biofilms

Background: An increasing prevalence of Candida infections has emerged with the wide use of immune-suppressants and antibiotics. Photodynamic inactivation (PDI) as a new approach to treat localized Candida infections is an emerging and promising field nowadays. This study evaluated the efficacy of photodynamic therapy using two new cationic benzylidene cyclopentanone photosensitizers (P1 and P2) against one strain of clinical fluconazole-resistant Candida albicans. Methods: Suspensions and biofilms of Candida species were incubated with P1 and P2 concentrations (0.25 similar to 50 mu M) for 30 min followed by 532nm laser irradiation. For planktonic suspensions, viability of cells was assayed by CFU counting. For biofilms, the metabolic activity was evaluated by XTT. Results: In PDI of a planktonic culture of clinical fluconazole-resistant C. albicans, P2 showed the higher efficacy. After incubation with 25 mu M of P2 for 30 min and irradiation with 532nm laser (36 J cm(-2)), the viability of C. albicans planktonic cells decreased by 3.84 log(10) (> 99.9% fungicidal activity). For biofilm cells, a higher light dose of 75 mW cm-2 was necessary to achieve 99.71% metabolic activity reduction. Conclusions: The results of this investigation demonstrated that benzylidene cyclopentanone photosensitizer(P2) is an efficient photosensitizer to kill C. albicans. Moreover, single-species biofilms were less susceptible to PDT than their planktonic counterparts.