Assessing probiotic Bacillus germination
Bacillus probiotics are now widely used in antibiotic- free production. Yet, evaluating the probiotic effect of individual strains on animal performance remains a challenge. Understanding their germination potential is a good place to start.
BY DR MARION BERNADEAU, PRINCIPAL SCIENTIST AT DANISCO ANIMAL NUTRITION (IFF) M
any of the probiotics used to supplement feed are of the Bacillus genus and this is largely due to their ability to produce spores. This natural phenomenon – known as sporulation – means
the bacteria undergo a three-stage lifecycle; where the inert spores germinate, proliferate into vegetative cells (VC) and then re-spore when nutrients are exhausted (Figure 1). And it gives Bacillus a distinct advantage over other non-spore former probiotic micro-organisms. By naturally transitioning from active to inert form, Bacillus can survive in nutrient-free and harsh environments.
Tracking germination
Various techniques are now used to assess Bacillus lifecycle, but all have pros and cons. By far most methods are categorised as direct, meaning they track spores or VC. Yet our review of published literature suggests that both exert probiotic benefits in the GIT. So this method does not present the full picture. Equally, the use of in vitro tubes to demonstrate germination of probiotic Bacillus spores is not appropriate as it doesn’t simulate all the physiological conditions encountered in the gut. And while it’s true that other research tools have demonstrated that Bacillus spores can germinate in intestinal conditions, they rely on GMOs, so are not applicable in commercial fields. To conclude, current methods of tracking germination in the GIT: • Lack accuracy and precision, both in terms of differentiating between spores and VC, and specific strains
• Fail to establish ratios between spores and VC • Are likely to use an engineered strain and lead to a GMO, so can only serve as a research tool.
For the customer, what matters most is that the effects of the Bacillus probiotic improve animal health and performance.
76 ▶ ANTIBIOTIC REDUCTION | DECEMBER 2021
Remarkably, they are resistant to chemicals, high temperatures, radiation, desiccation, and even predators. It is these inherent properties that enable them to withstand feed processing and storage conditions, as well as the challenging physiological barriers encountered in the gut. Crucially, not all probiotic Bacillus strains are the same. Which means that finding a strain that will deliver performance benefits to the animals not easy. It is vital that commercial products are supported by a detailed understanding of the unique behaviour and germination of the individual Bacillus strains. The three-strain Bacillus of Enviva PRO, for example, is the result of extensive screening, characterisation, and controlled sporulation on an industrial scale to ensure it maintains a high resistance to external factors until it is ingested by the animal. When it comes to evaluating the probiotic effect of spore- formers in the intestinal tract, there are also several points to keep in mind. First of all, sporulation is a reversible process. Secondly, spores and VC don’t have the same resistance profile against conditions encountered in the gut – VC are highly sensitive to stomach acidity and bile salt, whereas spores are unaffected. Equally important is the fact that spores and VC do not have the same functional properties.
Understanding germination To fully understand and maximise a probiotic’s efficacy, it’s necessary to first recognise that germination is a dependent process. Environmental conditions associated with different parts of the gastrointestinal tract (GIT) can influence the out- come. Oxygen and pH levels, nutrient availability and the presence of microbiota, as well as differences in transit time (rapid versus late germination), maturity of the intestinal tract and gut motility can all have an impact. Additional fac- tors include the size of the administered dose and choice of Bacillus strain. Given the sheer number of variables, it’s evident that not all probiotic strains will behave in the same way and differences in germination profile will occur between host specificities. Based on this rationale, we believe it is important to chal- lenge the assumption that one strain will follow the same pathway in different species. So how do you assess the germination potential of different Bacillus probiotics?
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