Evaluation of a Luminometric Cell Counting System in Context of Antimicrobial Photodynamic Inactivation

Abstract

Antimicrobial resistance belongs to the most demanding medical challenges, and antimicrobial photodynamic inactivation (aPDI) is considered a promising alternative to classical antibiotics. However, the pharmacologic characterization of novel compounds suitable for aPDI is a tedious and time-consuming task that usually requires preparation of bacterial cultures and counting of bacterial colonies. In this study, we established and utilized a luminescence-based microbial cell viability assay to analyze the aPDI effects of two porphyrin-based photosensitizers (TMPyP and THPTS) on several bacterial strains with antimicrobial resistance. We demonstrate that after adaptation of the protocol and initial calibration to every specific bacterial strain and photosensitizer, the luminometric method can be used to reliably quantify aPDI effects in most of the analyzed bacterial strains. The interference of photosensitizers with the luminometric readout and the bioluminescence of some bacterial strains were identified as possible confounders. Using this method, we could confirm the susceptibility of several bacterial strains to photodynamic treatment, including extensively drug-resistant pathogens (XDR). In contrast to the conventional culture-based determination of bacterial density, the luminometric assay allowed for a much more time-effective analysis of various treatment conditions. We recommend this luminometric method for high-throughput tasks requiring measurements of bacterial viability in the context of photodynamic treatment approaches.

Photodynamic Inactivation of SARS-CoV-2 Infectivity and Antiviral Treatment Effects In Vitro

“…If we compare required concentrations of THTPS and durations of PDI-activating illumination with those required for the inactivation of bacteria, especially multi-drugresistant critical Gram-negative strains like E. coli and Kleb. pneumoniae, we achieved inhibition of SARS-CoV-2 infectivity with much lower concentrations (0.3-1 µM compared to 200-400 µM) and much shorter illumination times (5-10 min compared to more than 100 min) [27,[30][31][32]. This may be caused by a higher susceptibility of virions to oxidative stress, since they lack systems that protect them from oxidative damage.…”