Background and aims: gut microbiota (GM) is a complex ecosystem containing bacteria, viruses, fungi, and yeasts. It has several functions in the human body ranging from immunomodulation to metabolic. GM derangement is called dysbiosis and is involved in several host diseases. Pre-, probiotics, and symbiotics (PRE-PRO-SYMB) have been extensively developed and studied for GM re-modulation. Herein, we review the literature data regarding the new concept of postbiotics, starting from PRE-PRO-SYMB. Methods: we conducted a search on the main medical databases for original articles, reviews, meta-analyses, randomized clinical trials, and case series using the following keywords and acronyms and their associations: gut microbiota, prebiotics, probiotics, symbiotic, and postbiotics. Results: postbiotics account for PRO components and metabolic products able to beneficially affect host health and GM. The deeper the knowledge about them, the greater their possible uses: the prevention and treatment of atopic, respiratory tract, and inflammatory bowel diseases. Conclusions: better knowledge about postbiotics can be useful for the prevention and treatment of several human body diseases, alone or as an add-on to PRE-PRO-SYMB.

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Background: Gut microbiota is a complex ecosystem of bacteria, viruses, archaea, protozoa and yeasts in our intestine. It has several functions, including maintaining human body equilibrium. Microbial “dysbiosis” can be responsible for outbreak of local and systemic infections, especially in critically ill patients. Methods: to build a narrative review, we performed a Pubmed, Medline and EMBASE search for English language papers, reviews, meta-analyses, case series and randomized controlled trials (RCTs) by keywords and their associations: critically ill patient; nutrition; gut microbiota; probiotics; gut virome; SARS-COV 2. Results: Over the antibiotic-based “selective decontamination”, potentially responsible for drug-resistant microorganisms development, there is growing interest of scientists and the pharmaceutical industry for pre-, probiotics and their associations as safe and reliable remedies restoring gut microbial “eubiosis”. Very first encouraging evidences link different gut microbiota profiles with SARS-COV 2 disease stage and gravity. Thus, there is frame for a probiotic therapeutic approach of COVID-19. Conclusions: gut microbiota remodulation seems to be a promising and safe therapeutic approach to prevent local and systemic multi-resistant bug infections in the intensive care unit (ICU) patients. This approach deserves more and more attention at the time of SARS-COV 2 pandemic.