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Probiotic origins, human residential and transient bacteria
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Microbiome and health: Demystifying probiotic origins

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The human microbiome is a dynamic and complex ecosystem that influences our wellbeing from early years and throughout life.

Microbes are all around us, living in and on us in a mutually beneficial relationship. They include bacteria, viruses, yeast, and fungi that inhabit our body in communities referred to as microbiomes, with the gut microbiome being the most complex and diverse.

The development of the human gut microbiome begins at birth and continues to evolve throughout a person’s life. It is not a static entity but remains dynamic, and various factors including diet, lifestyle, use of antibiotics, and environmental exposures can influence the composition and stability.

Scientific evidence is strongly suggesting that maintaining a well-balanced gut microbiome is important for our overall well-being. When this balance is disrupted, it can give rise to various health challenges, including digestive problems, allergies and a weakened immune system. But there is an opportunity to shape this delicate balance, especially during infancy but also later in life. Clinical research has demonstrated the significant impact of introducing specific probiotic strains during the first years of life and beyond. These beneficial microorganisms have shown the potential to restore and maintain a balanced gut microbiome, safeguarding health not just in those crucial early days, but throughout a lifetime.

What are probiotics?

Many food products and supplements contain live microorganisms, but only those containing characterized strains with a scientifically demonstrated effect on health may be termed ‘probiotic’.1

According to the World Health Organization’s 2014 definition, probiotics are ‘live microorganisms which, when administered in adequate amounts, confer a health benefit on the host’.2​ A probiotic is identified through its genus, species, and strain. Different strains of the same genus and species have been studied and shown to bring different health benefits, demonstrating how important the specific strain is.3

Despite growing consumer awareness of probiotics and the proliferation of probiotic products on the market, misconceptions still exist. Questions regarding how the origin of a probiotic strain impacts its effectiveness are frequently raised and discussed.

Where do probiotics originate from?

Probiotic strains are isolated from many sources in nature, typically including environmental samples, various food sources, such as fermented dairy products, and the human gastrointestinal tract (more commonly in the form of a faeces sample). As microbes are everywhere, it is important to remember we cannot assume or confer health benefits simply based on where probiotic strains were isolated from. Clinical documentation should be considered as the key factor for determining the efficacy of a probiotic strain, independent of its origin.

Transient and residential probiotic strains

Probiotic strains can be either residential or transient. Residential probiotic strains reside in the gut for a long period of time. Transient probiotic strains, also known as non-residential, do not colonize and establish in the body for an extended period of time. These enter the body from foods or certain dietary supplements and pass through the gastrointestinal system, where they may impact the microbiome, interacting with residential strains, pathogens, and even the immune system. Thus, both residential and transient strains may help restore balance in a permanent way.

An effective probiotic strain does not have to be capable of colonizing the human gastrointestinal tract for a long time  – indeed, most probiotics do not. Neither does a probiotic product need to be composed of multiple strains. There is no correlation between the number of strains and the efficacy of the product. Again, clinical documentation should be considered as the prime indicator.

But what can the source and naming of probiotic strains actually tell us about the probiotic and its effects on human health? How can bacteria from different origins be beneficial?

Demystifying probiotic origins – Spotlight On

In this Spotlight On broadcast, our experts will deep dive into the science and explore the common questions surrounding probiotic origins.

You will learn how residential and transient bacteria are not mutually exclusive and be presented with evidence of how both types of bacteria can play a part in contributing to a balanced microbiome. Moreover, our experts will drill down into the science behind clinical trials that have been conducted in infants and demonstrated beneficial effects of residential and transient bacteria in combination.

This is a must-attend event for anyone with an interest in improving their knowledge of probiotics. Join our expert speakers as they examine how the constant interaction with microorganisms found in natural surroundings has helped shape and establish dynamic ecosystems in our microbiomes over time and across life stages.

Join us for our Spotlight On broadcast ‘Demystifying probiotic origins: exploring the benefits of transient bacteria’, on 5 December, 10am CET. Register now


1. International Scientific Association for Probiotics and Prebiotics (ISAAP)​.
2. International Probiotics Association​.
3.​ McFarland LV, Evans CT, Goldstein EJC. Strain-Specificity and Disease-Specificity of Probiotic Efficacy: A Systematic Review and Meta-Analysis​. Front Med (Lausanne). 2018 May 7;5:124. doi: 10.3389/fmed.2018.00124. PMID: 29868585; PMCID: PMC5949321.

Additional references

Cho I.; Blaser MJ. The human microbiome: at the interface of health and disease​. Nat Rev Genet. 2012 Mar 13;13(4):260-70. doi: 10.1038/nrg3182. PMID: 22411464; PMCID: PMC3418802.