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Should the concept of postbiotics make us see probiotics from a new perspective?

By Dr. Gabriel Vinderola, PhD,  Associate Professor of Microbiology at the Faculty of Chemical Engineering from the National University of Litoral and Principal Researcher from CONICET at Dairy Products Institute (CONICET-UNL), Santa Fe, Argentina

In early May 2021 an ISAPP consensus panel  defined postbiotics as “a preparation of inanimate microorganisms and/or their components that confers a health benefit on the host“. The fact that non-viable microbes may still deliver health benefits is not new for the scientific community and was reviewed more than 20 years ago. More recent studies demonstrating health effects of non-viable microbes spurred interest in this topic, leading ISAPP to carefully consider the emerging use of the term ‘postbiotic’ and provide a clear, modern, concise definition.

Postbiotics can be contrasted with probiotics: live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. In practice, probiotics  have likely always coexisted with inanimate microbes, as live microbes will die at all phases of production of a product. In the past, it seems the presence of inanimate microbes as part of probiotic products was not really considered. We all knew they were there, but made a default assumption that they had limited significance. As we consider postbiotics, though, we should perhaps look again at how to address the inanimate components of probiotic products.

The presence of inanimate cells in probiotic preparations: from lab to product

A loop of a fresh, overnight, live culture of a probiotic strain may still contain non-viable cells (Fig. 1). During the biomass production of a probiotic culture, an abundance of live cells can be observed in the exponential growth phase, but as the culture enters the stationary phase, a significant increase in the proportion of non-viable cells occurs (Fig. 2). Yet the culture may display a satisfactory high number of viable cells as verified by traditional plating on agar media. Some years ago, it was reported that a fresh culture of a lactobacilli strain may display a live/dead cells ratio of ca. 100/1. However, this ratio may change to 1:1 after freeze-drying, as studied using flow cytometry, a technology that allows the quantification of both live and dead cells in a culture-independent way. Therefore, a recently freeze-dried culture of a probiotic strain may contain 1010 log CFU/g of live cells, but also the same amount of non-viable cells.

Food supplements may have a shelf life between 12 and 24 months at room temperature and over this time, a proportion of cells will likely lose viability along the shelf life. This depends on the intrinsic resistance of the strain, the nature of the matrix used for freeze-drying, the water activity remaining after lyophilization, the package and the storage conditions. Taking this into consideration, the probiotic supplements industry overfills probiotic capsules or sachets with 1.5 to 4 times more live cells, in order to warrant the delivery at the end of shelf life of the minimum amount of live cells to be able to deliver the expected health benefit. Considering that both freeze-drying and long-term storage may significantly increase the proportion of inanimate microorganisms in a probiotic supplement, a probiotic supplement could easily consist of more inanimate microorganisms than live ones. Yet if the products delivers the minimum amount of live cells to confer a health benefit, this makes the product fit the definition of probiotics so it must be considered a probiotic product. The probiotic focus has been prevalent during previous clinical trials and also during the shelf life of a probiotic product. Maybe we were just overlooking what was going on beyond the information obtained by CFU. These new insights do not change the status of a probiotic, but with due attention given to postbiotic components, offers the possibility to have better and better characterized products in the future.

Figure 1, above – Fluorescence microscopy images of an overnight (18h) culture of bifidobacteria (left) and lactobacilli (right) showing live (green) and non-viable cells (red). The Live/dead BackLight Invitrogen® kit was used for staining cells.

Figure 2, above – Fluorescence microscopy images of a culture of lactobacilli in the exponential (left) and late stationary (right) growth phase showing live (green) and non-viable cells (red). The Live/dead BackLight Invitrogen® kit was used for staining cells.

Are dead probiotics ‘postbiotics’?

What is the contribution of these inanimate cells to the overall health benefit observed for the probiotic culture? In most cases, no evidence exists documenting health benefits of inanimate probiotics. But we may have reason to suspect it may be relevant. For example, a live culture of Bifidobacterium bifidum MIMBb75 significantly alleviated irritable bowel syndrome symptoms and improved quality of life in a double-blind, placebo-controlled study when delivered at 109 CFU, but also the same strain performed equally well for the same end-point when delivered as a heat-inactivated culture. Also, a novel next-generation probiotic strain of Akkermansia muciniphila performed equally well in its live and pasteurized form for improving several metabolic parameters in overweight and obese volunteers. In these cases, it can be said that both strains fit simultaneously the probiotic and the postbiotic definitions.

However, does this mean that as the strain gradually loses viability during storage it gradually becomes a postbiotic? No! This is because method of strain inactivation may play an important role in the health benefit observed. For example, the health benefit delivered by a strain that underwent a heat inactivation can not be assumed to have the same functionality if it is left to die on its own on the shelves. A heat treatment may, for instance, modifiy the spatial display of surface proteins and this may lead to a different immunomodulating capacity of the strain when compared to spontaneous and gradual cell viability lost along storage.

Characterizing probiotic products with an eye to the presence of non-viable cells

By definition, probiotics must be quantified. In the past, this quantification has been limited to numbers of viable cells, typically using a colony count method. This is wholly appropriate, as probiotics must be alive. Yet for the future, will it become necessary to quantify the numbers of non-viable microbial cells as well? With evidence emerging that these non-viable cells may be functional components, then a reasonable argument can be made that this component of a probiotic product should also be quantified. This has implications for characterizing products for use in intervention trials and for the marketplace. The challenge for the marketplace is that probiotic products should deliver the functionality observed in intervention trials.

Reports of trials typically indicate a viable count of the probiotic being tested, but these can be reported in different ways. For example, the statement may indicate delivery of 1.9 × 107 CFU/day of the strain XXX, or delivery of > 1.9 × 107 CFU/day of the strain XXX. These are very different and neither gives any indication of the level of non-viable microbes. The first expression is a specific measure of the viable count at a particular point in time. The second indicates a target minimum and the actual count of viable cells could be much greater. Counts all along the intervention are rarely reported, even though that count could change substantively over time. Papers rarely report if the same batch or different batches of the probiotic preparation were used. The potentially increasing proportion of inanimate microbes is never reported.

In light of postbiotics, future studies should report quantifications of both live and inanimate microbes. Although it is not clear at this time what role inanimate microbes may play in probiotic efficacy, a first step is understanding the composition of probiotic products.

 

ISAPP members can access Dr. Vinderola’s webinar on this topic here. Email info@nullisappscience.org if you require the password.

What do we mean by ‘conferring a health benefit on the host’?

By Prof. Colin Hill, University College Cork, Ireland

Four of the Consensus definitions produced by ISAPP in recent years (see 1-4 below) finish with a similar wording, insisting that probiotics, prebiotics, synbiotics and postbiotics must confer a health benefit on the host”. This proviso was included to explicitly reinforce the fact that the raison d’etre for these interventions is that they must demonstrably improve host health. It would perhaps be wise to just stop there and leave the interpretation of what this really means to each individual reader. But that would not make for a very long blog and I am not very wise. Furthermore, it is useful to be more precise for scientific and regulatory purposes. At least two aspects seem to be open to elaboration; what is meant by ‘host’ and what is a ‘health benefit’? I will base my thoughts on the probiotic definition, but the logic should apply equally to all four health-based definitions.

Host. According to the Google dictionary a host is an animal or plant on or in which a parasite or commensal organism lives’. This means there are millions of potential host species on our planet, something that could potentially create confusion. For example, if a well characterised microbe (or microbes) is shown to provide a measurable health benefit when administered in adequate amounts in a murine model (the host) then it clearly meets the stated definition of probiotic. But only for mice! It should not be referred to as a probiotic for other species, including humans, solely based on murine evidence. This creates a situation where the same microbe can clearly meet the criteria to be a probiotic for one host but not for another. This is not simply semantics; it is of vital importance that it should not be assumed that health benefits confirmed in one host will also be realised in another without supporting evidence. Since the majority of discussions of probiotics address human applications, it may serve all stakeholders well – even if not directly mandated by the definition – if the word ‘probiotic’ was only used without qualification for microbes with measurable benefits in humans while all others should be qualified with the target host; ‘equine probiotic’, ‘canine probiotic’, or even ‘plant probiotic’.

Health benefit. Health is of course a continuum from a desirable but almost certainly unattainable state where every organ is performing optimally (something I will term ‘ideal health’) to a point where death is imminent (that I will term ‘poor health’). Of course, health is multidimensional and far more complex than a straight line between ‘ideal’ and ‘poor’ but for simplicity I will treat it as such. If we place ideal health on the left end of our straight line and poor health at the right end, then obviously any shift towards the left can be considered a health benefit. It could even be reasonably argued that if someone is gradually progressing from left to right down our imaginary line (for example, as we age) then halting or slowing down that progression could also be considered a health benefit. From this perspective every individual (not just the unwell) could potentially derive a health benefit from a probiotic, prebiotic, synbiotic or postbiotic.

The issue of cosmetic benefits is more nuanced. If an intervention improves someone’s appearance (or reduces body odour for example) it might not be considered a health benefit per se, but of course it could well have a beneficial effect on an individuals’ mental health. I will leave it to the psychologists and psychiatrists to determine how this could be convincingly demonstrated.

There is also the issue of production characteristics where the host is a food animal or a crop. If a microbial-based intervention leads to faster growth rates and increased yields should this qualify as a health benefit? My own opinion is if the intervention leads to higher productivity by preventing infections it could be considered a health benefit, but not if it simply leads to faster growth rates by improving feed conversion for example.

Can changing the microbiome be considered a health benefit? A trickier question is whether a direct effect on the microbiome could be considered as a health benefit? Every host has a microbiome of a particular configuration, richness, and diversity. I don’t think we are yet at a point where measurable changes in these general indices of microbiome composition can be termed a health benefit in the absence of a link to a more established health outcome. The consequence of any change will be microbiome-specific in any event; a reduction in diversity in the vaginal microbiome might be desirable, whereas an increase in diversity in the gut microbiome might well be considered beneficial. But what if we can measure a reproducible reduction in a specific pathobiont like Clostridioides difficile, or an increase in a microbe that is associated with good health such as Bifidobacterium? In my opinion we are arriving at a point where we can begin to refer to these impacts as a health benefit. This will become more and more relevant as we establish direct causal links between individual commensal microbes and health outcomes. Equally, an intervention that preserves microbiome structure during a disruption (e.g. infection or antibiotic treatment) could also be considered as beneficial. I don’t know if regulators are yet at the point of accepting outcomes such as these as direct health benefits, but I believe a strong case can be made.

To finish, I believe that it is a very exciting time for all of us in the field of probiotics, prebiotics, synbiotics and postbiotics, but it is really important that all of this important science is not compromised by loose language or by literal interpretations that adhere to the letter of the definitions but not to the intent. If you want to fully understand the intent of the definitions, I encourage you to read the full text of the consensus papers.

 

  1. https://doi.org/10.1038/nrgastro.2014.66
  2. https://doi.org/10.1038/nrgastro.2017.75
  3. https://doi.org/10.1038/s41575-020-0344-2
  4. https://doi.org/10.1038/s41575-021-00440-6

Follow up from ISAPP webinar – Probiotics, prebiotics, synbiotics, postbiotics and fermented foods: how to implement ISAPP consensus definitions

By Mary Ellen Sanders PhD, Executive Science Officer, ISAPP

On the heels of the most recent ISAPP consensus paper – this one on postbiotics – ISAPP sponsored a webinar for industry members titled Probiotics, prebiotics, synbiotics, postbiotics and fermented foods: how to implement ISAPP consensus definitions. This webinar featured short presentations outlining definitions and key attributes of these five substances. Ample time remained for the 10 ISAPP board members to field questions from attendees.

When considering the definitions, it’s important to remember that the definition is a starting point – not all criteria can be included. Using the probiotic definition as an example, Prof. Colin Hill noted that the definition is only 15 words – Live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. This is a useful definition, stipulating the core characteristics of a probiotic. However, important criteria such as safety and identity are not specified in the definition yet are clearly delineated in the full paper on probiotics.

Several interesting topics emerged from this discussion, which will be explored in future blog posts. These include:

  • What is meant by host health? Microbe mediated benefits are numerous. But not all benefits are a benefit to host health. Benefits for user appearance, pets and potentially livestock may be measurable, economically important and desirable, but may not encompass ‘host health’.
  • What types of endpoints are appropriate for studies to meet the requirement of a health benefit? Endpoints that indicate improved health (such as symptom alleviation, reduced incidence of infections or quality of life measures) are targeted. Some physiological measures that may be linked to health (such as increased fecal short chain fatty acids or changes in microbiota composition) may not be sufficient.
  • What are the regulatory implications from these definitions? As suggested by the National Law Review article on the ISAPP consensus definitions, attorneys are interested in the scientific positions on how these terms are defined and characterized. Further, some regulatory actions – such as by Codex Alimentarius in defining probiotics – are underway. ISAPP is open to suggestions about the best way to communicate these definitions to regulators.
  • Is any follow-up by ISAPP to these papers anticipated in order to clarify criteria and provide simple guidance to their implementation?

Simple guidance to these substances can be found in the infographics: probiotics, probiotic criteria, prebiotics, fermented foodshow are probiotic foods and fermented foods different, synbiotics, and postbiotics. As mentioned above, watch for blog updates on implementation of the definitions for different stakeholder groups.

The recording of this webinar is available here under password protection for ISAPP industry members only.

Related information:

Consensus panel papers, all published in Nature Reviews Gastroenterology and Hepatology:

A roundup of the ISAPP consensus definitions: probiotics, prebiotics, synbiotics, postbiotics and fermented foods

 

 

 

 

A roundup of the ISAPP consensus definitions: probiotics, prebiotics, synbiotics, postbiotics and fermented foods

By Dr. Mary Ellen Sanders, PhD, ISAPP Executive Science Officer

ISAPP has long recognized the importance of precise definitions of the ‘biotic’ family of terms. As a scientific organization working to advance global knowledge about probiotics, prebiotics, synbiotics, postbiotics and fermented foods, we believe carrying out rigorous scientific studies—and comparing one result to another—is more difficult if we do not start with a clear definition of what we are studying.

Over the past 8 years, ISAPP has endeavored to bring clarity to these definitions for scientists and other stakeholders. ISAPP board members have met with other top experts representing multiple perspectives and specialties in the field to develop precise, useful and appropriate definitions of the terms probiotics, prebiotics, synbiotics, postbiotics and fermented foods. The definitions of these first four terms have all entailed the requirement that the substance be shown to confer a health benefit in the target host. Fermented foods have multitudes of sensorial, nutritional and technological benefits, which drive their utility. A health benefit is not required.

The problem with health benefits

The definitions provide significant advantages for the scientific community in terms of clarity but complexity arises when the same definitions are accepted by regulatory agencies. This requirement for a health benefit as part of the probiotic definition has been rigorously implemented in the European Union. Currently, with the exception of a few member states, the term probiotic is prohibited. The logic is that since a health benefit is inherent to the term probiotic and since there are no approved health claims for probiotics in the EU*, the term ‘probiotic’ is seen to be acting as a proxy for a health claim. This has frustrated probiotic product companies who believe they have met the scientific criteria for probiotics, yet cannot identify their product as a probiotic in the marketplace because they have not received endorsement of their claims by the EU. This is not an issue resulting from an unclear definition, since probiotics surely should provide a health benefit, but rather from a lack of agreement as to what level of evidence is sufficient to substantiate a health benefit.

ISAPP remains committed to the importance of requiring a health benefit for the ‘biotic’ family of terms (outlined in the table below). It’s clear that all of these definitions are meaningless unless the requirement that they confer a health benefit is considered as essential by all stakeholders. One could reasonably discuss whether the required levels of evidence for foods and supplements are too high in some regulatory jurisdictions, but the value of these substances collapses in the absence of a health benefit.

Summary of ISAPP consensus definitions

With the publication of the most recent ISAPP consensus paper, this one on postbiotics, I offer a summary below of the five consensus definitions published by ISAPP. Each definition is part of a comprehensive paper resulting from focused discussions among experts in the field and published in Nature Reviews Gastroenterology and Hepatology (NRGH). These papers are among the top most viewed of all time on the NRGH website and are increasingly cited by scientists and regulators.

Table. Summary of ISAPP Consensus Definitions of the ‘Biotics’ Family of Substances. Probiotics, prebiotics, synbiotics and postbiotics have in common the requirement for a health benefit. They may apply to any target host, any regulatory category and must be safe for their intended use. Fermented foods fall only under the foods category and no health benefit is required.

Definition Key features of the definition Reference
Probiotics Live microorganisms that, when administered in adequate amounts, confer a health benefit on the host Grammatical correction of the 2001 FAO/WHO definition.

No mechanism is stipulated by the definition.

 

Hill et al. 2014
Prebiotics A substrate that is selectively utilized by host microorganisms conferring a health benefit Prebiotics are distinct from fiber. Beneficial impact on resident microbiota and demonstration of health benefit required in same study. Gibson et al. 2017
Synbiotics A mixture comprising live microorganisms and substrate(s) selectively utilized by host microorganisms that confers a health benefit on the host Two types of synbiotics defined: complementary and synergistic. Complementary synbiotics comprise probiotic(s) plus prebiotic(s), meeting requirements for criteria for each. Synergistic synbiotics comprise substrate(s) selectively utilized by co-administered live microbe(s), but independently, the components do not have to meet criteria for prebiotic or probiotic. Swanson et al. 2020
Postbiotics Preparation of inanimate microorganisms and/or their components that confers a health benefit on the host Postbiotics are prepared from live microbes that undergo inactivation and the cells or cellular structures must be retained. Filtrates or isolated components from the growth of live microbes are not postbiotics. A probiotic that is killed is not automatically a postbiotic; the preparation must be shown to confer a health benefit, as well as meet all other criteria for a postbiotic. Salminen et al. 2021
Fermented Foods Foods made through desired microbial growth and enzymatic conversions of food components Fermented foods are not the same as probiotics. They are not required to have live microbes characterized to the strain level nor have evidence of a health benefit. Types of fermented foods are many and are specific to geographic regions. Compared to the raw foods they are made from, they may have improved taste, digestibility, safety, and nutritional value. Marco et al. 2021

 

 

*Actually, there is one approved health claim in the EU for a probiotic: Scientific Opinion on the substantiation of health claims related to live yoghurt cultures and improved lactose digestion (ID 1143, 2976) pursuant to Article 13(1) of Regulation (EC) No 1924/2006

 

Further reading: Defining emerging ‘biotics’

New publication addresses the question: Which bacteria truly qualify as probiotics?

Although the international scientific consensus definition of probiotics, published in 2014, is well known—”live microorganisms that, when administered in adequate amounts, confer a health benefit on the host”—the word is often used incorrectly in practice.

A recent article published in Frontiers in Microbiology builds on this definition and describes four criteria for accurate use of the word ‘probiotic’. Eight scientists co-authored the paper, including two ISAPP board members. The project was initiated by industry scientists affiliated with IPA Europe.

The authors explain why it’s important for scientists and companies to be sure the four identified criteria apply before using the term ‘probiotic’. Given the many misuses of the term that are evident today, however, consumers need to scrutinize ‘probiotic’ products to be sure they are legitimate.

Read the ISAPP press release on this publication here.

See an infographic summary of this publication here.

 

 

The FDA’s view on the term probiotics, part 1

By James Heimbach, Ph.D., F.A.C.N., JHEIMBACH LLC, Port Royal, VA

James Heimbach, food and nutrition regulatory consultant

Over the past 20 years as a food and nutrition regulatory consultant, I have filed about 40 GRAS notices with the United States Food and Drug Administration (FDA), including 15 strains of probiotic bacteria and 5 prebiotics. This fall I submitted notices dealing with 4 strains of bacteria and on January 16 received a telephone call from FDA that surprised me and initially infuriated me, but which I have come to understand.

The essence of the call was that FDA was declining to file my probiotic notices because the notices had identified the subject bacteria as “probiotics” or “probiotic bacteria.” FDA suggested that I resubmit without calling the subject microorganisms “probiotics.”

 

 

As I said, I was surprised and frustrated, and I still would prefer that when FDA makes a policy swerve they would do it in a way that does not make extra work for me and delay my clients’ ability to get to market in a timely manner.

What I have had to do here is remove my advocate’s hat and put on my regulator’s hat. (I worked for FDA for a decade . . . long ago [1978 to 1988], but I still remember how to think like a regulator.) And here is the issue. Recall that GRAS is concerned with safety, not efficacy (generally recognized as safe, or GRAS), and the information provided in a GRAS notice is focused on safety (although benefits may be more-or-less incidentally covered). The reviewers at FDA are charged with assessing whether the notice provides an adequate basis to conclude that there is a reasonable certainty that no harm will result from the intended use. They are not charged, and they are not equipped, to evaluate what benefits ingestion of the substance or microorganism might provide. So they are not in a position to say whether the subject microorganism will “confer a health benefit on the host,” which is to say, they are not in a position to say whether or not it may be regarded as a probiotic. Remember, probiotics are defined as live microorganisms that, when administered in adequate amounts, confer a health benefit on the host (Hill et al. 2014).

Given that the FDA reviewers cannot say whether the notified microorganism is rightly called a probiotic, they are reluctant to sign off that they have no questions about a notice that calls it one. Regulatory agencies have to be careful; things sometimes come back to haunt them. Those who have been following FDA’s GRAS-notice response letters for a couple of decades will be aware that the agency is putting more and more disclaimers into the letters—about standards of identity, about potential labeling issues, about benefits shown in clinical trials, and about Section 201(II) of the FD&C Act.

One concern that FDA likely has is that if some issue comes up in the future regarding a claim made for benefits from use of a product containing the subject bacterium, someone may make the argument that FDA had accepted that the strain is indeed a probiotic and so it presumably confers probiotic benefits. In the case of probiotics, there are also some internal FDA politics. As ISAPP meeting attendees may already be aware, FDA’s Center for Biologics Evaluation and Research (CBER) would like to claim jurisdiction over all administration of live microorganisms, and the Center for Food Safety and Applied Nutrition (CFSAN) does not seem willing to have a confrontation.

I suspect that a similar situation obtains with the term “prebiotic.” Although I have filed a number of GRAS notices for prebiotics, they haven’t been called that; they have been called fructooligosaccharides, or tamarind seed polysaccharide, or polydextrose, or 2’-O-fucosyllactose. I don’t know how FDA would respond if a GRAS determination were filed with the substance labeled as a prebiotic.

So, I’ve decided that my sympathies lie with FDA. Until and unless a microorganism has been confirmed by competent authority to have probiotic properties when used as intended in a GRAS notice, FDA is probably correct in rejecting its right to be labeled a probiotic. If it’s any consolation, this new position by the FDA has its origin in their acknowledgment of the official scientific definition of the word “probiotic”.

When Mary Ellen Sanders (ISAPP’s Executive Science Officer) reviewed my first draft of this note, she asked what I had in mind by “competent authority,” to which I don’t have a good answer at the present time except to insist that it is not FDA’s Division of GRAS Notice Review. Thirty years ago, when I was at FDA, I was in the Office of Food Science and Nutrition, and that office was charged with making determinations of that type (although I don’t recall anything about probiotics coming before us). But FDA no longer has such an office. Until it does, or until it agrees on another source of authority on designation of microorganisms as non-CBER-domain probiotics, I suspect that CFSAN will continue to be very cautious in this area.

Read part 2 of this blog series here.