Bacterial Photodynamic Inactivation: Eradication of Staphylococcus aureus and Escherichia coli Mediated by Pyridinium-Pyrazolyl Zinc(II) Phthalocyanines

Antimicrobial resistance remains an enduring global health issue, manifested when microorganisms, such as bacteria, lack responsiveness to antimicrobial treatments. Photodynamic inactivation (PDI) of microorganisms arises as a noninvasive, nontoxic, and repeatable alternative for the inactivation of a broad range of pathogens. So, this study reports the synthesis, structural characterization, and photophysical properties of a new tetra-β-substituted pyridinium–pyrazolyl zinc(II) phthalocyanine (ZnPc 1a ) that was compared with two previously described pyridinium–pyrazolyl ZnPcs 2a and 3a . The PDI efficacy of these three ZnPcs ( 1a – 3a ) against a drug-resistant Gram-positive bacterium (as Staphylococcus aureus ) and a Gram-negative bacterium (as Escherichia coli ) is also reported. The PDI efficacy toward these bacteria was examined with ZnPcs 1a – 3a in the 5.0–10.0 μM range using a white light source with an irradiance of 150 mW/cm 2 . All ZnPcs displayed a significant PDI activity against S. aureus, with reductions superior to 3 Log CFU/mL. Increasing the treatment time, the E. coli was inactivated until the detection limit of the method (>6.3 Log CFU/mL) using the quaternized ZnPcs 1a – 3a (10.0 μM, 120 min) being the inactivation time was reduced when added the KI for ZnPcs 1a and 3a . These findings demonstrate the effective PDI performance of pyridinium–pyrazolyl group-bearing PSs, indicating their potential use as a versatile antimicrobial agent for managing infections induced by Gram-negative and Gram-positive bacteria.