Shaping the Future of Probiotics and Prebiotics

An expanding range of candidate probiotic species and prebiotic substrates is emerging to address newly elucidated data-driven microbial niches and host targets.Overlapping with, and adjacent to, the probiotic and prebiotic fields, new variants of microbiome-modulating interventions are developing, including synbiotics, postbiotics, microbial consortia, live biotherapeutic products, and genetically modified organisms, with renewed interest in polyphenols, fibres, and fermented foods.Personalised nutrition and precision medicine are beginning to influence the application of probiotics and prebiotics, with growing interest in modulation of microbial signatures of health and disease.Demand for probiotics and prebiotics across divergent product formats is driving innovation in quality assurance techniques to measure dose, viability, and structural and functional integrity. Recent and ongoing developments in microbiome science are enabling new frontiers of research for probiotics and prebiotics. Novel types, mechanisms, and applications currently under study have the potential to change scientific understanding as well as nutritional and healthcare applications of these interventions. The expansion of related fields of microbiome-targeted interventions, and an evolving landscape for implementation across regulatory, policy, prescriber, and consumer spheres, portends an era of significant change. In this review we examine recent, emerging, and anticipated trends in probiotic and prebiotic science, and create a vision for broad areas of developing influence in the field. Recent and ongoing developments in microbiome science are enabling new frontiers of research for probiotics and prebiotics. Novel types, mechanisms, and applications currently under study have the potential to change scientific understanding as well as nutritional and healthcare applications of these interventions. The expansion of related fields of microbiome-targeted interventions, and an evolving landscape for implementation across regulatory, policy, prescriber, and consumer spheres, portends an era of significant change. In this review we examine recent, emerging, and anticipated trends in probiotic and prebiotic science, and create a vision for broad areas of developing influence in the field. Probiotics (see Glossary) and prebiotics have received escalating attention in recent years in the scientific, healthcare, and public arenas. Publicity around microbiome research has also broadened the public perception of microorganisms, beyond disease-causing agents that should be avoided, to a more rational view integrating an understanding of the beneficial roles of microorganisms in human health. In line with these advances, public awareness and acceptance of probiotics and prebiotics continues to expand [1.Chin-Lee B. et al.Patient experience and use of probiotics in community-based health care settings.Patient Prefer. Adhere. 2014; 8: 1513-1520PubMed Google Scholar], with probiotic industry growth estimated at 7% annually [2.Jackson S.A. et al.Improving end-user trust in the quality of commercial probiotic products.Front. Microbiol. 2019; 10: 739Crossref PubMed Scopus (19) Google Scholar], and prebiotic growth forecast at 12.7% over the next 8 years [3.Mano M.C.R. et al.Oligosaccharide biotechnology: an approach of prebiotic revolution on the industry.Appl. Microbiol. Biotechnol. 2018; 102: 17-37Crossref PubMed Scopus (40) Google Scholar]. While there is a general consumer view that probiotics and prebiotics are beneficial, there is still a gap in understanding on definitions of the terms 'probiotics' and 'prebiotics', their benefits to health, how they function, and where to find the best sources in food and healthcare products [1.Chin-Lee B. et al.Patient experience and use of probiotics in community-based health care settings.Patient Prefer. Adhere. 2014; 8: 1513-1520PubMed Google Scholar,4.Viana J.V. et al.Probiotic foods: consumer perception and attitudes.Int. J. Food Sci. Technol. 2008; 43: 1577-1580Crossref Scopus (30) Google Scholar]. Both probiotics and prebiotics are increasingly incorporated into a wide range of foods, beverages, and topical products (even toilet paper), in some cases with questionable or no scientific validation of any health benefit to the host, as is the requirement of existing consensus definitions. In this scientific field, definitions for both are clearly established, with the International Scientific Association for Probiotics and Prebiotics (ISAPP) having convened consensus panels whereby experts reviewed and published the science behind probiotics [5.Hill C. et al.Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic.Nat. Rev. Gastroenterol. Hepatol. 2014; 11: 506-514Crossref PubMed Scopus (2566) Google Scholar] and prebiotics [6.Gibson G.R. et al.Expert consensus document: The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics.Nat. Rev. Gastroenterol. Hepatol. 2017; 14: 491-502Crossref PubMed Scopus (1252) Google Scholar]. The conclusions of these panels highlighted that they play an integral role in health status. Some key mechanisms have been elucidated (Box 1) and both have been used in a variety of health states, prophylactically and therapeutically.Box 1Mechanisms of Action of Probiotics and PrebioticsMechanisms of action of probiotics and prebiotics are complex, diverse, heterogeneous, and often strain- and compound-specific. While many have been described, there remain calls for increased understanding, especially structure–function explanations of observed health effects and long-term influences [134.Kleerebezem M. et al.Understanding mode of action can drive the translational pipeline towards more reliable health benefits for probiotics.Curr. Opin. Biotechnol. 2019; 56: 55-60Crossref PubMed Scopus (26) Google Scholar,152.Plaza-Diaz J. et al.Mechanisms of action of probiotics.Adv. Nutr. 2019; 10: S49-S66Crossref PubMed Scopus (96) Google Scholar,153.Monteagudo-Mera A. et al.Adhesion mechanisms mediated by probiotics and prebiotics and their potential impact on human health.Appl. Microbiol. Biotechnol. 2019; 103: 6463-6472Crossref PubMed Scopus (91) Google Scholar].Probiotics interact with both the host and the microbiome via molecular effectors present on the cell structure or secreted as metabolic products. Probiotic metabolites can act on the microbiota by crossfeeding interactions, changes in the gastrointestinal microenvironment (e.g., pH lowering), competition for nutrients and binding sites, and inhibition of growth via the production of strain-specific antibacterial compounds including bacteriocins [133.Lebeer S. et al.Identification of probiotic effector molecules: present state and future perspectives.Curr. Opin. Biotechnol. 2018; 49: 217-223Crossref PubMed Scopus (90) Google Scholar,152.Plaza-Diaz J. et al.Mechanisms of action of probiotics.Adv. Nutr. 2019; 10: S49-S66Crossref PubMed Scopus (96) Google Scholar,153.Monteagudo-Mera A. et al.Adhesion mechanisms mediated by probiotics and prebiotics and their potential impact on human health.Appl. Microbiol. Biotechnol. 2019; 103: 6463-6472Crossref PubMed Scopus (91) Google Scholar]. Such microbiota-directed effects contribute to the ability of probiotics to mediate health benefits in pathogen overgrowth states such as vaginal and oral dysbioses [153.Monteagudo-Mera A. et al.Adhesion mechanisms mediated by probiotics and prebiotics and their potential impact on human health.Appl. Microbiol. Biotechnol. 2019; 103: 6463-6472Crossref PubMed Scopus (91) Google Scholar].With regard to host cells, probiotic effector molecules can interact directly with receptors in intestinal epithelial, enteroendocrine, and immune cells as well as vagal afferent fibres. These interactions produce local gut effects, such as enhancement of intestinal barrier integrity and inflammation (e.g., via Toll-like receptors), as well as systemic effects via host immune, endocrine, and nervous system mediators [133.Lebeer S. et al.Identification of probiotic effector molecules: present state and future perspectives.Curr. Opin. Biotechnol. 2018; 49: 217-223Crossref PubMed Scopus (90) Google Scholar,152.Plaza-Diaz J. et al.Mechanisms of action of probiotics.Adv. Nutr. 2019; 10: S49-S66Crossref PubMed Scopus (96) Google Scholar,153.Monteagudo-Mera A. et al.Adhesion mechanisms mediated by probiotics and prebiotics and their potential impact on human health.Appl. Microbiol. Biotechnol. 2019; 103: 6463-6472Crossref PubMed Scopus (91) Google Scholar]. Probiotics can also perform enzymatic metabolism of host compounds such as bile salts and ingested xenobiotics [152.Plaza-Diaz J. et al.Mechanisms of action of probiotics.Adv. Nutr. 2019; 10: S49-S66Crossref PubMed Scopus (96) Google Scholar]. Specific probiotic surface-associated effector molecules include pili, lipoteichoic acids, exopolysaccharides, and various surface-layer proteins, many of which are strain-specific and therefore mediate the delivery of strain-specific effects [133.Lebeer S. et al.Identification of probiotic effector molecules: present state and future perspectives.Curr. Opin. Biotechnol. 2018; 49: 217-223Crossref PubMed Scopus (90) Google Scholar,153.Monteagudo-Mera A. et al.Adhesion mechanisms mediated by probiotics and prebiotics and their potential impact on human health.Appl. Microbiol. Biotechnol. 2019; 103: 6463-6472Crossref PubMed Scopus (91) Google Scholar].Classical prebiotic effects are mediated through consumption of the substrate by specific groups within the microbiota, promoting their growth and metabolic activity. Provision of substrate to select group/s of bacteria can also indirectly influence other bacterial groups within the microbiome – promoting growth through crossfeeding interactions as well as inhibitory effects via pathogen displacement. Resulting changes in microbial composition and metabolite concentrations from prebiotic administration impact host epithelial, immune, nervous, and endocrine signalling and mediate health benefits such as improvements in bowel function, immune response, glucose and lipid metabolism, bone health, and regulation of appetite and satiety [6.Gibson G.R. et al.Expert consensus document: The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics.Nat. Rev. Gastroenterol. Hepatol. 2017; 14: 491-502Crossref PubMed Scopus (1252) Google Scholar]. Chief by-products of bacterial prebiotic metabolism are the SCFAs acetate, butyrate, and propionate, which are well recognised to interact with these host systems and facilitate many prebiotic effects [10.Blaak E.E. et al.Short chain fatty acids in human gut and metabolic health.Benefic. Microbes. 2020; 11: 411-455Crossref PubMed Scopus (3) Google Scholar].In addition to nutritive effects on microbes, prebiotic molecules are also recognised to interact directly with host receptors, modulating immune and gut epithelial cell signalling with local effects on inflammation and barrier function [154.Brosseau C. et al.Prebiotics: mechanisms and preventive effects in allergy.Nutrients. 2019; 11: 1841Crossref Scopus (6) Google Scholar]. Mechanisms of action of probiotics and prebiotics are complex, diverse, heterogeneous, and often strain- and compound-specific. While many have been described, there remain calls for increased understanding, especially structure–function explanations of observed health effects and long-term influences [134.Kleerebezem M. et al.Understanding mode of action can drive the translational pipeline towards more reliable health benefits for probiotics.Curr. Opin. Biotechnol. 2019; 56: 55-60Crossref PubMed Scopus (26) Google Scholar,152.Plaza-Diaz J. et al.Mechanisms of action of probiotics.Adv. Nutr. 2019; 10: S49-S66Crossref PubMed Scopus (96) Google Scholar,153.Monteagudo-Mera A. et al.Adhesion mechanisms mediated by probiotics and prebiotics and their potential impact on human health.Appl. Microbiol. Biotechnol. 2019; 103: 6463-6472Crossref PubMed Scopus (91) Google Scholar]. Probiotics interact with both the host and the microbiome via molecular effectors present on the cell structure or secreted as metabolic products. Probiotic metabolites can act on the microbiota by crossfeeding interactions, changes in the gastrointestinal microenvironment (e.g., pH lowering), competition for nutrients and binding sites, and inhibition of growth via the production of strain-specific antibacterial compounds including bacteriocins [133.Lebeer S. et al.Identification of probiotic effector molecules: present state and future perspectives.Curr. Opin. Biotechnol. 2018; 49: 217-223Crossref PubMed Scopus (90) Google Scholar,152.Plaza-Diaz J. et al.Mechanisms of action of probiotics.Adv. Nutr. 2019; 10: S49-S66Crossref PubMed Scopus (96) Google Scholar,153.Monteagudo-Mera A. et al.Adhesion mechanisms mediated by probiotics and prebiotics and their potential impact on human health.Appl. Microbiol. Biotechnol. 2019; 103: 6463-6472Crossref PubMed Scopus (91) Google Scholar]. Such microbiota-directed effects contribute to the ability of probiotics to mediate health benefits in pathogen overgrowth states such as vaginal and oral dysbioses [153.Monteagudo-Mera A. et al.Adhesion mechanisms mediated by probiotics and prebiotics and their potential impact on human health.Appl. Microbiol. Biotechnol. 2019; 103: 6463-6472Crossref PubMed Scopus (91) Google Scholar]. With regard to host cells, probiotic effector molecules can interact directly with receptors in intestinal epithelial, enteroendocrine, and immune cells as well as vagal afferent fibres. These interactions produce local gut effects, such as enhancement of intestinal barrier integrity and inflammation (e.g., via Toll-like receptors), as well as systemic effects via host immune, endocrine, and nervous system mediators [133.Lebeer S. et al.Identification of probiotic effector molecules: present state and future perspectives.Curr. Opin. Biotechnol. 2018; 49: 217-223Crossref PubMed Scopus (90) Google Scholar,152.Plaza-Diaz J. et al.Mechanisms of action of probiotics.Adv. Nutr. 2019; 10: S49-S66Crossref PubMed Scopus (96) Google Scholar,153.Monteagudo-Mera A. et al.Adhesion mechanisms mediated by probiotics and prebiotics and their potential impact on human health.Appl. Microbiol. Biotechnol. 2019; 103: 6463-6472Crossref PubMed Scopus (91) Google Scholar]. Probiotics can also perform enzymatic metabolism of host compounds such as bile salts and ingested xenobiotics [152.Plaza-Diaz J. et al.Mechanisms of action of probiotics.Adv. Nutr. 2019; 10: S49-S66Crossref PubMed Scopus (96) Google Scholar]. Specific probiotic surface-associated effector molecules include pili, lipoteichoic acids, exopolysaccharides, and various surface-layer proteins, many of which are strain-specific and therefore mediate the delivery of strain-specific effects [133.Lebeer S. et al.Identification of probiotic effector molecules: present state and future perspectives.Curr. Opin. Biotechnol. 2018; 49: 217-223Crossref PubMed Scopus (90) Google Scholar,153.Monteagudo-Mera A. et al.Adhesion mechanisms mediated by probiotics and prebiotics and their potential impact on human health.Appl. Microbiol. Biotechnol. 2019; 103: 6463-6472Crossref PubMed Scopus (91) Google Scholar]. Classical prebiotic effects are mediated through consumption of the substrate by specific groups within the microbiota, promoting their growth and metabolic activity. Provision of substrate to select group/s of bacteria can also indirectly influence other bacterial groups within the microbiome – promoting growth through crossfeeding interactions as well as inhibitory effects via pathogen displacement. Resulting changes in microbial composition and metabolite concentrations from prebiotic administration impact host epithelial, immune, nervous, and endocrine signalling and mediate health benefits such as improvements in bowel function, immune response, glucose and lipid metabolism, bone health, and regulation of appetite and satiety [6.Gibson G.R. et al.Expert consensus document: The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics.Nat. Rev. Gastroenterol. Hepatol. 2017; 14: 491-502Crossref PubMed Scopus (1252) Google Scholar]. Chief by-products of bacterial prebiotic metabolism are the SCFAs acetate, butyrate, and propionate, which are well recognised to interact with these host systems and facilitate many prebiotic effects [10.Blaak E.E. et al.Short chain fatty acids in human gut and metabolic health.Benefic. Microbes. 2020; 11: 411-455Crossref PubMed Scopus (3) Google Scholar]. In addition to nutritive effects on microbes, prebiotic molecules are also recognised to interact directly with host receptors, modulating immune and gut epithelial cell signalling with local effects on inflammation and barrier function [154.Brosseau C. et al.Prebiotics: mechanisms and preventive effects in allergy.Nutrients. 2019; 11: 1841Crossref Scopus (6) Google Scholar]. Currently, multiple spheres of influence are acting on the probiotic and prebiotic fields (Figure 1). Broad technological advances in data collection and analytical tools are enabling the exploration of new candidate probiotics and prebiotics as well as providing deeper insights into their interactions with the microbiome and host. Interest continues to grow into new applications of probiotics and prebiotics across health conditions, body sites, population subgroups, and delivery formats. Furthermore, evolution in regulatory frameworks, clinical guidelines and industry trends is influencing the implementation of probiotics and prebiotics into nutrition and healthcare. As our knowledge continues to expand in each of these fields, a broad and integrated review of trends shaping the future of probiotics and prebiotics is timely. Traditionally, lactobacilli, bifidobacteria, and other lactic acid-producing bacteria (LAB) have been used as probiotics, primarily isolated from fermented dairy products and the faecal microbiome. As knowledge of the breadth of the human microbiome and its functions has expanded, the future holds a range of potential new discovery approaches [7.Veiga P. et al.Moving from probiotics to precision probiotics.Nat. Microbiol. 2020; 5: 878-880Crossref PubMed Scopus (5) Google Scholar] as well as new potential probiotic taxa. Developments in affordable complete genome sequencing and powerful cultivation methods have allowed isolation and characterisation of a new range of microorganisms from human microbiomes with potential health benefits and the opportunity to be developed as next-generation probiotics [8.O'Toole P.W. et al.Next-generation probiotics: the spectrum from probiotics to live biotherapeutics.Nat. Microbiol. 2017; 2: 17057Crossref PubMed Scopus (213) Google Scholar] (Figure 2). Various bacteria, such as Roseburia intestinalis, Faecalibacterium prausnitzii, Eubacterium spp., Bacteroides spp. and Akkermansia muciniphila, have been isolated from the human gut with growing interest in their probiotic potential [8.O'Toole P.W. et al.Next-generation probiotics: the spectrum from probiotics to live biotherapeutics.Nat. Microbiol. 2017; 2: 17057Crossref PubMed Scopus (213) Google Scholar,9.Brodmann T. et al.Safety of novel microbes for human consumption: practical examples of assessment in the European Union.Front. Microbiol. 2017; 8: 1725Crossref PubMed Scopus (64) Google Scholar]. These candidates represent a significant proportion of the currently cultivable human gut microbiome and offer physiological functions that are not always directly conferred by bifidobacteria or lactobacilli, such as the production of butyrate, propionate, and other bioactives [10.Blaak E.E. et al.Short chain fatty acids in human gut and metabolic health.Benefic. Microbes. 2020; 11: 411-455Crossref PubMed Scopus (3) Google Scholar]. Converting these species into industrially viable probiotics presents challenges as their requirement for rich growth media and anaerobic conditions adds cost and complexity, as well as investment in determining optimal fermentation and manufacturing processes over time. Despite these difficulties, A. muciniphila is one of the more promising candidates. Isolated in 2004 [11.Derrien M. et al.Akkermansia muciniphila gen. nov., sp. nov., a human intestinal mucin-degrading bacterium.Int. J. Syst. Evol. Microbiol. 2004; 54: 1469-1476Crossref PubMed Scopus (843) Google Scholar], it has been tested in preclinical animal models and shown to prevent development of obesity, with bacterial pasteurisation increasing stability and efficacy of the species. Initial proof-of-concept studies have taken place in humans and shown that both live and pasteurised A. muciniphila is safe to use in humans and improves several metabolic parameters [12.Depommier C. et al.Supplementation with Akkermansia muciniphila in overweight and obese human volunteers: a proof-of-concept exploratory study.Nat. Med. 2019; 25: 1096-1103Crossref PubMed Scopus (332) Google Scholar]. Live A. muciniphila is already on the market in a multispecies synbiotic preparation, containing inulin, Bifidobacterium longum subsp. infantis and other anaerobic bacteria (Clostridium beijerinckii, Clostridium butyricum, and Anaerobutyricum hallii) and was shown to improve glucose levels in type 2 diabetics [13.Perraudeau F. et al.Improvements to postprandial glucose control in subjects with type 2 diabetes: a multicenter, double blind, randomized placebo-controlled trial of a novel probiotic formulation.BMJ Open Diabetes Res. Care. 2020; 8e001319Crossref PubMed Scopus (1) Google Scholar]. The gut microbiome will not be the only source of new candidate probiotic strains (Figure 1). Niches of strong interest for discovery of new species, and as targets for intervention, include the female urogenital tract, oral cavity, nasopharyngeal tract, and skin [14.Maguire M. Maguire G. The role of microbiota, and probiotics and prebiotics in skin health.Arch. Dermatol. Res. 2017; 309: 411-421Crossref PubMed Scopus (24) Google Scholar, 15.George V.T. et al.The promising future of probiotics: a new era in periodontal therapy.J. Int. Oral Heal. 2016; 8: 404-408Google Scholar, 16.Cribby S. et al.Vaginal microbiota and the use of probiotics.Interdiscip. Perspect. Infect. Dis. 2008; 2008 (art. 256490)Crossref PubMed Google Scholar]. Species or genera associated with health in these regions are being investigated as potential interventions to restore microbial populations and therefore physiological homeostasis in disease states. Examples include the skin commensal isolate Staphylococcus hominis for eczema and atopic dermatitis [17.Nakatsuji T. et al.Antimicrobials from human skin commensal bacteria protect against Staphylococcus aureus and are deficient in atopic dermatitis.Sci. Transl. Med. 2017; 9eaah4680Crossref PubMed Scopus (362) Google Scholar], and Lactobacillus crispatus for vaginal dysbiosis [18.Reid G. Probiotic and prebiotic applications for vaginal health.J. AOAC Int. 2012; 95: 31-34Crossref PubMed Scopus (29) Google Scholar]. Fermented foods are the most common natural source of potentially probiotic strains of LAB, and consumption has been associated with significant health benefits, including reduced risk of type 2 diabetes and cardiovascular diseases [19.Marco M.L. et al.Health benefits of fermented foods: microbiota and beyond.Curr. Opin. Biotechnol. 2017; 44: 94-102Crossref PubMed Scopus (363) Google Scholar] as well as a putatively beneficial metabolomic profile [20.Taylor B.C. et al.Consumption of fermented foods is associated with systematic differences in the gut microbiome and metabolome.mSystems. 2020; 5e00901-19Crossref PubMed Scopus (13) Google Scholar]. These foods are most likely the major source of LAB in the human gut microbiome [21.Pasolli E. et al.Large-scale genome-wide analysis links lactic acid bacteria from food with the gut microbiome.Nat. Commun. 2020; 11: 2610Crossref PubMed Scopus (24) Google Scholar] and show potential for future probiotic development. Fermented and unfermented food sources of future probiotics may include fruits, vegetables, grains/cereals, dairy, meat and fish products, and honey, as well as environmental sources such as soil [22.Zielińska D. Kolożyn-Krajewska D. Food-origin lactic acid bacteria may exhibit probiotic properties: Review.Biomed. Res. Int. 2018; 2018 (art. 5063185)Crossref Scopus (24) Google Scholar]. In addition to the core heartlands of gut and immune health, emerging target conditions for probiotic therapy include subfertility [23.García-Velasco J.A. et al.What fertility specialists should know about the vaginal microbiome: a review.Reprod. BioMed. Online. 2017; 35: 103-112Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar], liver disease [24.Meroni M. et al.The role of probiotics in nonalcoholic fatty liver disease: a new insight into therapeutic strategies.Nutrients. 2019; 11: 2642Crossref Scopus (6) Google Scholar], mood disorders [25.Dinan T.G. et al.Psychobiotics: a novel class of psychotropic.Biol. Psychiatry. 2013; 74: 720-726Abstract Full Text Full Text PDF PubMed Scopus (510) Google Scholar], cognition [26.Dinan T.G. Cryan J.F. The microbiome–gut–brain axis in health and disease.Gastroenterol. Clin. N. Am. 2017; 46: 77-89Abstract Full Text Full Text PDF PubMed Google Scholar], oral health [27.Seminario-Amez M. et al.Probiotics and oral health: A systematic review.Med. Oral Patol. Oral Cir. Bucal. 2017; 22: e282-e288PubMed Google Scholar], asthma [28.Spacova I. et al.Probiotics against airway allergy: host factors to consider.Dis. Models Mech. 2018; 11dmm034314Crossref PubMed Scopus (3) Google Scholar], metabolic disease [29.Koutnikova H. et al.Impact of bacterial probiotics on obesity, diabetes and non-alcoholic fatty liver disease related variables: a systematic review and meta-analysis of randomised controlled trials.BMJ Open. 2019; 9e017995Crossref PubMed Scopus (65) Google Scholar], hypercholesterolaemia [30.Khare A. Gaur S. Cholesterol-lowering effects of Lactobacillus species.Curr. Microbiol. 2020; 77: 638-644Crossref PubMed Scopus (7) Google Scholar], and obesity [31.Brusaferro A. et al.Is it time to use probiotics to prevent or treat obesity?.Nutrients. 2018; 10: 1613Crossref Scopus (39) Google Scholar]. Significant emphasis will be placed on investigating the safety of novel species and genera considered for the development of new probiotic products [8.O'Toole P.W. et al.Next-generation probiotics: the spectrum from probiotics to live biotherapeutics.Nat. Microbiol. 2017; 2: 17057Crossref PubMed Scopus (213) Google Scholar,9.Brodmann T. et al.Safety of novel microbes for human consumption: practical examples of assessment in the European Union.Front. Microbiol. 2017; 8: 1725Crossref PubMed Scopus (64) Google Scholar]. Many commonly exploited and currently available probiotic strains benefit from a generally recognized as safe (GRAS) status in the USA or belong to species with qualified presumption of safety (QPS) status with the European Food Safety Authority (EFSA), yet this is not yet the case for other candidate novel probiotic species that have no history of use. Submission through GRAS, QPS, and novel food frameworks may enable a path to commercialisation, and for pharmaceutical applications, novel regulatory frameworks are emerging, for example, the live biotherapeutic products category being defined by the Food and Drug Administration (FDA)i and the European Directorate for the Quality of Medicines [32.European Pharmacopoeia Commission 3053E General monograph on live biotherapeutic products.Eur. Pharmacopoeia. 2019; (9.7)Google Scholar]. A complete characterisation of strains from these new species will likely be required [33.Rouanet A. et al.Live biotherapeutic products, a road map for safety assessment.Front. Med. 2020; 7: 237Crossref PubMed Scopus (3) Google Scholar], comprising retrospective analysis of possible human disease linked with the taxa considered, full genome sequence, antibiotic resistance genes, toxin genes, transferrable genetic elements, virulence factors, proven safety in animal models, pharmacokinetics, pharmacodynamics, and Phase I–III trials. Many live biotherapeutic products with appropriate clinical evidence will fall within the current scientific definition of probiotics [5.Hill C. et al.Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic.Nat. Rev. Gastroenterol. Hepatol. 2014; 11: 506-514Crossref PubMed Scopus (2566) Google Scholar] (Figure 2), albeit attracting specific regulatory attention. The discovery of defined therapeutic microbial consortia with network interactions and synergistic effects [34.Vázquez-Castellanos J.F. et al.Design of synthetic microbial consortia for gut microbiota modulation.Curr. Opin. Pharmacol. 2019; 49: 52-59Crossref PubMed Scopus (8) Google Scholar] will augment the development of single-strain organisms in the future and remain in the scope of the current probiotic definition, if well characterised [5.Hill C. et al.Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic.Nat. Rev. Gastroenterol. Hepatol. 2014; 11: 506-514Crossref PubMed Scopus (2566) Google Scholar] (Figure 2). Adjacent to probiotics, postbiotics 1An updated expert consensus panel definition, convened by ISAPP, is currently in press. – microbial fragments and metabolites [35.Aguilar-Toalá J. et al.Postbiotics: An evolving