The Role of Probiotics and Their Postbiotic Metabolites in Post-COVID-19 Syndrome.

Post-COVID-19 syndrome, also known as long-COVID, is characterized by a wide spectrum of persistent symptoms involving multiple body organs and systems, including fatigue, gastrointestinal disorders, and neurocognitive dysfunction. Emerging evidence suggests that gut microbiota dysbiosis and disruption of the gut-brain axis play a central role in the pathophysiology of this condition. Probiotics and their metabolites (postbiotics) have gained increasing attention as potential therapeutic agents given their immunomodulatory, anti-inflammatory, and antiviral properties. In this review, we discuss the current understanding of the antiviral mechanisms of probiotics, including reinforcement of intestinal epithelial barrier function, direct virus inhibition, receptor competition, and immune system modulation. Special emphasis is placed on short-chain fatty acids (SCFAs), lactic acid, hydrogen peroxide, and bacteriocins as key factors that contribute to these effects. SCFAs appear to be essential postbiotic compounds during post-COVID recovery. We also highlight recent clinical trials involving specific probiotic species, such as Lactiplantibacillus plantarum, Lacticaseibacillus rhamnosus, and Bifidobacterium longum, and their potential role in alleviating long-term COVID symptoms. Although the current results are promising, further research is needed to clarify the most effective strains, dosages, and mechanisms of action in post-COVID therapeutic strategies.