Nano-Hypericin Therapy Reduces S. mutans Viability

Researchers evaluated a combined antimicrobial strategy targeting Streptococcus mutans, a major pathogen responsible for dental caries. The study, published in AMB Express, investigated the antimicrobial and anti-virulence potential of nano-hypericin-mediated antimicrobial photodynamic therapy combined with a postbiotic derived from Lactobacillus casei. This approach aims to address the growing challenge of antibiotic resistance by offering a non-antibiotic alternative for modulating cariogenic bacterial pathogenicity under in vitro conditions.

The experimental design involved the synthesis and characterization of nano-hypericin, referred to as nHyp. Using transmission electron microscopy, UV-Vis spectroscopy, and dynamic light scattering, the team confirmed that the nanoparticles were quasi-spherical with an average size of approximately 47 nanometers. Concurrently, the Lactobacillus casei-derived postbiotic, designated PSLC, was purified via acid precipitation. Chemical profiling through gas chromatography-mass spectrometry revealed that PSLC contains a diverse mixture of diketopiperazines, fatty acids, hydrocarbons, and phenolic compounds.

Planktonic Streptococcus mutans were treated with nHyp at concentrations ranging from 1.9 to 1000 micrograms per milliliter. These treatments were applied with or without blue laser irradiation at a wavelength of 450 plus or minus 5 nanometers for durations between 1 and 5 minutes.

Bacterial viability was measured by quantifying colony forming units per milliliter, while the expression of the gtfB gene was analyzed using quantitative reverse transcription polymerase chain reaction. The gtfB gene is relevant to glucan synthesis, a process critical for biofilm formation. By measuring both viability and gene expression, the study provided a comprehensive view of how the treatments affected bacterial survival and virulence factors.

The results demonstrated that nHyp-mediated antimicrobial photodynamic therapy induced dose- and time-dependent reductions in bacterial viability. The maximum reduction in viability observed with this therapy alone was up to 81 percent. When the postbiotic PSLC was added to the treatment regimen, the antimicrobial effect was further enhanced, achieving a maximum reduction in viability of up to 90.5 percent.

Regarding anti-virulence effects, sub-lethal antimicrobial photodynamic therapy using a concentration of 15.6 micrograms per milliliter of nHyp and a 2-minute irradiation period downregulated gtfB expression by 4.25-fold. When this sub-lethal treatment was combined with PSLC, the suppression of gtfB expression increased to 7.86-fold. This significant downregulation suggests that the combination therapy effectively inhibits glucan synthesis, thereby potentially reducing the ability of S. mutans to form biofilms.

The study highlights the promise of a dual-mechanism, antibiotic-free approach to managing dental caries. The findings are based on in vitro conditions, meaning that the results reflect laboratory observations rather than clinical outcomes in human patients.

As antibiotic resistance continues to pose a threat to public health, the development of non-antibiotic strategies is essential.

Subject of Research: In vitro evaluation of nano-hypericin photodynamic therapy and postbiotic effects on Streptococcus mutans

Article Title: Combined nano-hypericin antimicrobial photodynamic therapy and postbiotic on Streptococcus mutans

Article References: Ghasemi, N., Pourhajibagher, M., Azizi, A., & Bahador, A. (2026). Combined nano-hypericin antimicrobial photodynamic therapy and postbiotic on Streptococcus mutans. AMB Express, 16(1), Article 105. https://doi.org/10.1186/s13568-026-02097-3

Image Credits: AI Generated

DOI: 10.1186/s13568-026-02097-3

Keywords: Streptococcus mutans, Antimicrobial photodynamic therapy, Nano-hypericin, Postbiotic, Dental caries, gtfB expression, In vitro study, AMB Express, Combined, antimicrobial, photodynamic, therapy