In this study, we present the draft genome sequence of the Enterococcus sp. strain SB12, which was isolated from artisanal cheese of the Carpathian region (Ukraine). The de novo assembly produced 64 contigs, with a total length of 2,514,601 bp. Phylogenetic analysis revealed its proximity to the Enterococcus faecium strains.

The gastrointestinal microbiome plays a central role in host physiology, and the predominance of beneficial microorganisms is associated with improved metabolic and immune functions. Enterococci are natural members of the gut microbiota and are known to produce enterocins with antimicrobial activity against various pathogenic bacteria, thereby modulating microbial community structure. This study investigates the metabolic potential of Enterococcus sp. SB12, including vitamin and amino acid profiles, as well as its effects on intestinal microbiome composition, blood biochemistry, and oxidative stress markers in mice. Vitamin and amino acid profiles were analyzed by HPLC in bacterial biomass, as well as in the growth medium before and after cultivation of Enterococcus sp. SB12. Twenty one-month-old female mice were divided into control and experimental groups (n = 10 per group). The experimental group received Enterococcus sp. SB12 daily in drinking water at a dose of 1 × 10⁸ CFU/g body weight for 29 days. Gut microbiota composition was assessed using 16S rRNA gene and ITS2 sequencing, and biochemical and oxidative stress parameters were determined in blood and tissues. HPLC analysis of bacterial biomass detected several biologically important vitamins, including vitamins B1, B3, B5, B6, and C, together with amino acids such as valine (9.27 mg/g), cysteine (5.80 mg/g), glutamine (5.34 mg/g), proline (4.47 mg/g), and taurine (2.82 mg/g). Metataxonomic analysis revealed an increased relative abundance of Enterococcus in the experimental group, which may be consistent with persistence of enterococci in the gastrointestinal tract. Administration of SB12 was associated with an increased relative abundance of Enterococcus and several Firmicutes-associated taxa, accompanied by a reduced relative abundance of members of the family Desulfovibrionaceae and Helicobacter-associated taxa compared with the control group. Mice receiving SB12 exhibited significantly higher body weight than controls (28.1 ± 1.05 vs. 27.2 ± 0.82 g; p < 0.05), whereas visceral fat mass, organ weights, blood glucose, total protein, HDL cholesterol, LDL cholesterol, and oxidative stress markers did not differ significantly between groups. Overall, administration of Enterococcus sp. SB12 was associated with compositional changes in the intestinal microbiome and did not induce detectable alterations in biochemical or oxidative stress parameters. These findings provide preliminary evidence supporting the probiotic potential and safety of Enterococcus sp. SB12 under the experimental conditions used; however, additional studies are required to confirm its long-term safety profile and functional effects on the host.

The study analyzes the effect of the probiotic strain Enterococcus sp. SB12 on the antioxidant defense system of mice. The relevance of the study is due to the need to search for new strains capable of modulating the redox status without depleting the internal resources of the host organism. The experiment was conducted on white laboratory mice, which were orally administered a suspension of the studied strain for 28 days. The state of the oxidative-antioxidant balance was assessed by the intensity of lipid peroxidation (content of hydroperoxides and TBA-reactive substances, the level of protein carbonyls, and catalase activity. It was found that long-term use of Enterococcus sp. SB12 does not cause significant changes in the content of lipoperoxidation products and carbonyl groups of proteins, which indicates the absence of a prooxidant effect on cellular structures. Catalase activity remained at the level of the control group, indicating a stable state of the enzymatic defense chain and the absence of metabolic stress. It was found that Enterococcus sp. SB12 does not disturb the balance of free radicals and is characterized by high metabolic safety, which makes it promising for use in probiotic preparations.