Current Microbiology · 5 authors, 2 centres
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This study demonstrates that hyaluronic acid (HA) produced by the probiotic strains Enterococcus durans K11 and Lactiplantibacillus plantarum St3 exhibits antioxidant activity and protects human dermal keratinocytes from UVB-induced damage. Pre-treatment with these HA extracts maintained cell viability at 91.3% and 91.4%, respectively, compared to 76% in untreated irradiated cells, suggesting potential as a natural photoprotective agent.
**Background:** Overexposure to UV radiation, particularly UVB, causes oxidative stress, DNA damage, and skin photoaging. Hyaluronic acid (HA) is a natural polysaccharide with antioxidant properties that may protect skin. This study aimed to isolate probiotic bacteria capable of producing HA and evaluate its photoprotective effects on human keratinocytes.
**Methods:** Eighteen bacterial isolates were obtained from kefir and breast milk samples, along with four reference probiotic strains. HA production was screened using a turbidimetric CTAB assay and confirmed by HPLC. The two highest producers were identified by 16S rRNA sequencing as Enterococcus durans strain K11 and Lactiplantibacillus plantarum strain St3. HA was extracted from fermented skimmed milk, purified, and characterized by FTIR. Antioxidant activity was measured by DPPH radical scavenging assay. For photoprotection, human dermal keratinocytes were exposed to a single UVB dose of 10 mJ/cm². Cells were either pre-treated with HA (1 mg/ml) before irradiation or post-treated immediately after. Cell viability was assessed by MTT assay after 24 hours.
**Key Results:** The highest HA producers were K11 (E. durans) and St3 (L. plantarum), yielding 4.8±0.3 mg/ml and 4.4±0.2 mg/ml by HPLC, respectively. FTIR spectra confirmed HA identity. DPPH scavenging activity was 65.4±0.2% for K11 HA and 66.6±0.1% for St3 HA. UVB irradiation reduced viability of untreated cells to 76%. Pre-treatment with K11 HA and St3 HA maintained viability at 91.3% and 91.4%, respectively, significantly higher than untreated cells (p≤0.05). Post-treatment with K11 HA and St3 HA resulted in viabilities of 86% and 88.5%, respectively, also significantly better than untreated cells. Both produced HAs showed significantly better protection than commercial HA in pre-treatment (p≤0.05).
**Clinical Implications:** This study identifies two novel probiotic strains, E. durans K11 and L. plantarum St3, as safe (GRAS) HA producers with antioxidant and photoprotective properties. The HA extracts significantly reduced UVB-induced keratinocyte death, suggesting potential as natural ingredients in sunscreens or after-sun care products. Further in vivo studies are needed to confirm efficacy and safety for topical use.