Photodynamic inactivation of Staphylococcus aureus in the presence of aggregation-prone photosensitizers based on BODIPY used at submicromolar concentrations

ElsevierVolume 235, October 2022, 112543Journal of Photochemistry and Photobiology B: BiologyHighlights•

Two new bromo-BODIPY derivatives capable of generating singlet oxygen upon irradiation have been synthesized and characterized.

In an aqueous environment, those photosensitizers tend to aggregate leading to nanoparticles.

Compound 2 caused a 3 log CFU reduction at a concentration of only 0.16 μM for S. aureus

Compound 1 was effective to induce a 3 log CFU reduction of S. aureus at a concentration of only 0.32 μM

This is the first case of “one-for-all" approach to combat pathogenic bacteria using bodipy photosentizers.

Abstract

Two new brominated BODIPYs (1 and 2) bearing amino acid-based chains (l-valine for 1, and dimethyl-l-lysine for 2) were synthesized and characterized. In organic solvents, 1 and 2 were fully soluble and showed the photophysical properties expected for brominated BODIPY dyes, including efficient generation of singlet oxygen (1O2), upon irradiation. In contrast, in aqueous media, both compounds were prone to aggregation and the photo-induced generation of 1O2 was halted. Despite the lack of generation of this reactive species in aqueous media (in cuvette), both 1 and 2 have positive antimicrobial Photodynamic Inactivation (aPDI) effect. The activity against gram-positive Staphylococcus aureus and gram-negative Escherichia coli was determined through the inactivation curves, with a total energy dose of 5.3 J/cm2 (white light LED used as an energy source). Compound 2 was highly active against both gram-positive and gram-negative bacteria (3 log CFU/mL reduction was obtained at 0.16 μM for S. aureus and 2.5–5.0 μM for E. coli), whereas 1 was less effective to kill S. aureus (3 log CFU/mL at 0.32 μM) and ineffective for E. coli. The higher efficiency of 2, as compared to 1, to reduce the population of bacteria, can reside in the presence of a protonatable residue in 2, allowing a more effective interaction of this molecule with the cell walls of the microorganisms. In order to explain the lack of reactivity in pure aqueous media (in cuvette) and the contrasting good activity in the presence of bacterial cells it can be hypothesized that upon interaction with the walls of the microorganisms, the aggregated photosensitizers suffer a disaggregation process restoring the ability to generate 1O2, and hence leading to efficient photodynamic activity against these pathogenic microorganisms, in agreement with the similar effect observed recently for porphyrinoid photosensitizers.

Keywords

Photodynamic inactivation

Photo-antimicrobials

Singlet oxygen

Photosensitizers

S. aureus

E. coli

ESKAPE

© 2022 The Authors. Published by Elsevier B.V.

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