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<p>Dental caries is a prevalent microbial disease, with <i>Streptococcus mutans</i> as a major pathogen. Increasing antibiotic resistance highlights the need for alternative, non-antibiotic strategies. This study evaluated the antimicrobial and anti-virulence potential of nano-hypericin (nHyp)-mediated antimicrobial photodynamic therapy (aPDT) combined with <i>Lactobacillus casei</i>-derived postbiotic (PS<sup>LC</sup>). nHyp was synthesized and characterized by transmission electron microscopy, UV–Vis spectroscopy, and dynamic light scattering, confirming quasi-spherical nanoparticles (~ 47&#xa0;nm). PS<sup>LC</sup> was purified via acid precipitation and chemically profiled by gas chromatography–mass spectrometry, revealing diketopiperazines, fatty acids, hydrocarbons, and phenolic compounds. Planktonic <i>S. mutans</i> were treated with nHyp (1.9–1000&#xa0;µg/mL) ± blue laser irradiation (450 ± 5&#xa0;nm, 1–5&#xa0;min), alone or combined with PS<sup>LC</sup> at 1/2 × MIC (32&#xa0;µg/mL). Bacterial viability was measured by colony forming unit (CFU)/mL, and <i>gtfB</i> expression quantified by qRT-PCR. nHyp-mediated aPDT induced dose- and time-dependent reductions in bacterial viability (up to 81%), further enhanced by PS<sup>LC</sup> (up to 90.5%). Sub-lethal aPDT (15.6&#xa0;µg/mL + 2&#xa0;min) downregulated <i>gtfB</i> 4.25-fold, whereas combination with PS<sup>LC</sup> achieved 7.86-fold suppression, indicating inhibition of glucan synthesis relevant to biofilm formation. These findings demonstrate that nHyp-mediated aPDT combined with PS<sup>LC</sup> enhances antimicrobial and anti-virulence effects under in vitro conditions, representing a promising dual-mechanism, antibiotic-free approach to modulate cariogenic bacterial pathogenicity.</p>

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

  • 期刊论文

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  • 发表日期：

    2026年7月31日

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  • Narges Ghasemi,
  • Maryam Pourhajibagher,
  • Arash Azizi,
  • Abbas Bahador

摘要

Dental caries is a prevalent microbial disease, with Streptococcus mutans as a major pathogen. Increasing antibiotic resistance highlights the need for alternative, non-antibiotic strategies. This study evaluated the antimicrobial and anti-virulence potential of nano-hypericin (nHyp)-mediated antimicrobial photodynamic therapy (aPDT) combined with Lactobacillus casei-derived postbiotic (PSLC). nHyp was synthesized and characterized by transmission electron microscopy, UV–Vis spectroscopy, and dynamic light scattering, confirming quasi-spherical nanoparticles (~ 47 nm). PSLC was purified via acid precipitation and chemically profiled by gas chromatography–mass spectrometry, revealing diketopiperazines, fatty acids, hydrocarbons, and phenolic compounds. Planktonic S. mutans were treated with nHyp (1.9–1000 µg/mL) ± blue laser irradiation (450 ± 5 nm, 1–5 min), alone or combined with PSLC at 1/2 × MIC (32 µg/mL). Bacterial viability was measured by colony forming unit (CFU)/mL, and gtfB expression quantified by qRT-PCR. nHyp-mediated aPDT induced dose- and time-dependent reductions in bacterial viability (up to 81%), further enhanced by PSLC (up to 90.5%). Sub-lethal aPDT (15.6 µg/mL + 2 min) downregulated gtfB 4.25-fold, whereas combination with PSLC achieved 7.86-fold suppression, indicating inhibition of glucan synthesis relevant to biofilm formation. These findings demonstrate that nHyp-mediated aPDT combined with PSLC enhances antimicrobial and anti-virulence effects under in vitro conditions, representing a promising dual-mechanism, antibiotic-free approach to modulate cariogenic bacterial pathogenicity.