Photoinactivation of MRSA ATCC 33591 by antimicrobial photodynamic therapy using coumarin-functionalized zinc(II) phthalocyanine.

This study evaluates the photodynamic inactivation potential of a coumarin-functionalized zinc(II) phthalocyanine derivative against methicillin-resistant Staphylococcus aureus (MRSA) ATCC 33591. The antimicrobial and cytotoxic effects of the derivative were assessed under dark and laser-irradiated (658 nm) conditions. Minimum inhibitory concentration (MIC) values were determined, and the photodynamic response was further explored in MRSA-infected HT-29 (human colorectal adenocarcinoma) and HUVEC (human umbilical vein endothelial) cell models. While the derivative exhibited dose-dependent antibacterial activity, the light-induced reduction in colony-forming units (CFU) was moderate, remaining below a tenfold (1-log10) under the tested conditions. In cell-based assays, the compound showed detectable dark cytotoxicity, which was further enhanced upon laser irradiation. The photodynamic cytotoxic response was more pronounced in infected HT-29 cells than in infected HUVEC cells, with flow-cytometric profiles consistent with predominantly necrotic/late apoptotic cell-death patterns. These findings indicate that the compound exhibits light-enhanced effects in complex infection models; however, further optimization of formulation, photophysical properties, and light dosimetry is required to improve antimicrobial efficacy and selectivity.