This blog post provides an introduction to the recently published paper from Journal of Water & Health, and highlights some of the key features and findings of the research.

Hydrogen peroxide preoxidation as a strategy for enhanced antimicrobial photodynamic action against methicillin-resistant Staphylococcus aureus

doi.org/10.2166/wh.2023.245

By Kamila Jessie Sammarro Silva, Mariana de Souza, Thalita H. N. Lima, Alessandra R. Lima

Antibiotic resistance is one of the main challenges in public health in the 21st century. It is mostly due to prolonged and/or inadequate use of antibiotics. These, along with antibiotic resistant bacteria, get into municipal and hospital wastewaters, and may be spread into water sources by inefficient disinfection. Antimicrobial photodynamic treatment (aPDT) may be an alternative to tackle the issue of antimicrobial resistance spread.

The photodynamic process occurs when a photosensitizer molecule (PS) is excited by light at a specific wavelength. The PS then generates reactive oxygen species, which attack biomolecules, leading to cell death. This ability to inactivate microorganisms without being selective is an advantage to fight antibiotic resistant bacteria and has been used in infection control. Recently, photodynamic action has gained attention in water and wastewater treatment, inviting enhanced applications.

Hydrogen peroxide (H2O2) is a very popular disinfectant in the food industry and in clinical environments. In previous research on combined application of aPDT and H2O2, a satisfactory performance was not found and results pointed to antagonistic effects by including H2O2 immediately before illumination. Here, we performed a follow-up study testing sequential treatment, that is: incubating contaminated samples with the PS along with H2O2, and only then illuminating samples with blue light. This paper describes the inactivation of methicillin-resistant Staphylococcus aureus (MRSA) by preoxidation with H2O2 followed by aPDT using curcumin, a vegetal-based PS. Both the preoxidant and the PS present low environmental toxicity at the concentrations explored in this study.

Results suggested that this protocol provides a synergistic effect after a breakpoint, which means that the presence of the oxidant agent impairs the performance of the photodynamic process, and, from a certain concentration on, leads to improved inactivation. The synergistic effects indicate that results of sequential treatment are better than the sum of oxidation by H2O2 and photodynamic treatment when performed alone. We believe that preoxidation by H2O2 makes bacterial cells more susceptible to photodynamic action.

Although aPDT has been most widely explored within the clinical context for therapies against infections, it is important to highlight the potential for its applications in the environmental sector. The prospects of aPDT to contribute to mitigating problems related to the spread of antibacterial resistance in the environment are outstanding, especially considering enhanced treatments. However, our study was carried out in-vitro, under laboratory conditions, and some deeper challenges may apply, as in:

  • Tests against other pathogen groups;
  • Matrix effect (color, turbidity, suspended solids, etc.);
  • Up-scaling;
  • Optimizing operational conditions;
  • Biofilms, etc.

The proposed method for sequential treatment relies on environmental-friendly solutions for both applied chemicals and the illumination source. The study highlights the relevance of aPDT as a tool in addressing challenges related to the spread of antimicrobial resistance in aquatic environments, encouraging an integrated approach for water and wastewater disinfection technologies.

You can read the full paper here.

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