Bioactive fractions from Streptococcus macedonicus MBF 10-2 produced in an optimized plant-based peptone medium

Postbiotic fractions of lactic acid bacteria have been reported for their potential applications as skin health's microbial therapeutics and may also appeal to consumers who wish to avoid animal-based products. We aim to establish the optimum plant-peptone fermentation of Streptococcus macedonicus MBF10-2, which possesses Bacteriocin Like-Inhibitory Substance activity in our previous study, to produce bacterial bioactive fractions. We evaluate their potential antibacterial and antioxidant actions and assess the preliminary safety for human skin application. Fermentation was carried out using plant peptone modified de Man, Rogosa, and Sharpe (MRS) medium, i.e., soy peptone and Vegitone, non-animal-carbon sources that substitute proteose peptone in MRS medium. Fractions of MBF10-2 lysate and cell-free supernatant were collected and processed as follows, i.e., cell disruption, fraction separation, and fractions freeze-drying. Fractions were confirmed for antibacterial properties by the agar well diffusion method and assess for antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH), while safety assessment was carried out by skin patch assay. Maximum growth of MBF10-2 achieved by fermentation in soy peptone- and in Vegitone-modified media was 9.00 and 7.99 g total cell mass, respectively. The antibacterial property of fractions was most effective against Micrococcus luteus T18. The lysate fraction exhibited a mild antioxidant potency (IC50 840 µg/mL), and all bioactive fractions were proven safe and non-allergenic for human skins. S. macedonicus MBF10-2 postbiotics bioactive fractions were indicated as being safe for topical application. This is the first report on the production of a safe S. macedonicus bioactive postbiotic possessing mild antibacterial and mild-to-weak antioxidant.