Enterococcus in herbal fermentation: a genus-specific perspective on enzymatic capability, biotransformation outcomes and safety.

Although Enterococcus species are consistently detected in traditional herbal fermentations, their functional contributions to medicinal plant biotransformation remain poorly characterised at the genus level. This review provides the first genus-specific synthesis of Enterococcus in medicinal and food-medicinal plant fermentation, integrating evidence across historical fermentation systems, microbial ecology, enzymatic capability, phytochemical transformation, and safety assessment. Enterococcus species frequently occupy an early-to-middle ecological niche in fermented herbal matrices, sustained by exceptional tolerance to acidic, saline, and polyphenol-rich conditions. This ecological fitness is coupled to a functionally diverse enzymatic repertoire-encompassing β-glucosidases, α-rhamnosidases, ferulic acid esterases, tannases, bile salt hydrolases, and phenolic acid decarboxylases-capable of targeting the major glycosidic, ester, amide, and carboxylate linkages present in plant secondary metabolite conjugates. Documented biotransformations include ginsenoside Rb1-to-F2 conversion, sequential flavonoid diglycoside hydrolysis, ellagic acid-to-urolithin A transformation, gallotannin degradation, and oxalate catabolism-reactions that collectively parallel key TCMs processing objectives of bioavailability enhancement, pharmacological activation, and toxicity reduction. Safety challenges, particularly the concentration of virulence factors and transferable antibiotic resistance in E. faecalis and E. faecium, are critically evaluated. Mitigation strategies-including whole-genome-based strain screening, heat-inactivated postbiotic preparations, and recombinant enzyme platforms-are discussed as viable pathways toward controlled, safety-validated medicinal applications. The evidence supports a fundamental reappraisal of Enterococcus as a mechanistically distinctive contributor to herbal fermentation. Future progress will require strain-resolved functional characterisation, multi-omics-guided analysis, and safety-validated bioprocess design. This review is intended for researchers in fermentation microbiology, natural-product biotransformation, and the modernisation of traditional medicine, as well as for those engaged in the safety evaluation of fermentation-associated bacteria.