Enhanced photoinduced antibacterial activity of a BODIPY photosensitizer in the presence of polyamidoamines.

Photosensitizers belonging to the boron-dipyrromethenes (BODIPYs) class were recently found endowed with good efficacy in the antibacterial photodynamic therapy (aPDT) against both Gram-positive and Gram-negative bacteria. In this paper, we report on the remarkable adjuvant effect exerted in this respect by linear polyamidoamines (PAAs), a family of moderately basic polymers obtained by Michael-type polyaddition of amines to bisacrylamides. Three different PAAs (AGMA1, BP-AGMA, and BP-DMEDA) were studied, testing for each two different molecular weight samples (8000 and 24000 Da). At nontoxic concentrations (1 or 10 µg mL-1) all PAAs remarkably improved the killing efficacy of BODIPY upon irradiation with a green LED device (range: from 480 to 580 nm with λmax = 525 nm) up to an energy rate of 16.6 J cm-2. A 6-7 log unit decrease in bacteria survival was observed with concentrations of BODIPY of 1.0 and 0.1 µM in the case of Escherichia coli and Staphylococcus aureus, respectively. The one-way analysis of variance (ANOVA) was used to evaluate the statistical significance of different treatments (n ≥ 3). Thus, the PAA-photosensitizer combination warrants potentially as a new, effective, and mild method of killing bacteria. Moreover, the antibacterial treatment here reported might be successfully applied to defeat the bacterial resistance often encountered with many antibacterial drugs owing to the double action of this two-component treatment.