Antimicrobial photodynamic activity of toluidine blue encapsulated in mesoporous silica nanoparticles against Pseudomonas aeruginosa and Staphylococcus aureus

Abstract

In the present study, the antimicrobial and antibiofilm efficacy of toluidine blue (TB) encapsulated in mesoporous silica nanoparticles (MSN) was investigated against Pseudomonas aeruginosa and Staphylococcus aureus treated with antimicrobial photodynamic therapy (aPDT) using a red diode laser 670 nm wavelength, 97.65 J cm⁻² radiant exposure, 5 min). Physico-chemical techniques (UV-visible (UV-vis) absorption, photoluminescence emission, excitation, and FTIR) and high-resolution transmission electron microscopy (HR-TEM) were employed to characterize the conjugate of TB encapsulated in MSN (TB MSN). TB MSN showed maximum antimicrobial activities corresponding to 5.03 and 5.56 log CFU ml⁻¹ reductions against P. aeruginosa and S. aureus, respectively, whereas samples treated with TB alone showed 2.36 and 2.66 log CFU ml⁻¹ reductions. Anti-biofilm studies confirmed that TB MSN effectively inhibits biofilm formation and production of extracellular polymeric substances by P. aeruginosa and S. aureus.

Keywords:

• Antimicrobial photodynamic therapy
• anti-biofilm
• encapsulation
• mesoporous silica nanoparticles
• photosensitizer
• reactive oxygen species
• toluidine blue

Acknowledgements

The authors are grateful to the Central Instrumentation Facility (CIF) of Pondicherry University and the Department of Physics, Pondicherry University. The authors would also like to extend their sincere appreciation to King Saud University, Deanship of Scientific Research, College of Sciences, Research Centre for supporting this research. The authors are also grateful to Bharathidasan University, Tiruchirappalli for providing the confocal laser scanning microscope facility.

Disclosure statement

No conflict of interest is declared by the authors.