The long rise to fame - probiotics ascend to essential tools for poultry health

Preface

Disease pressure on poultry flocks is mounting from all sides, with re-emerging diseases like E. cecorum, existing ones like E. coli becoming more of a commercial issue, and food safety adding greater scrutiny on potential zoonotic pathogens like Salmonella sp. While in the past coccidiosis and clostridia control were the chief concerns, these additional issues increase the need to treat with antibiotics. However, antibiotics in all applications, humans, poultry and livestock, are under pressure from lack of efficacy, and there are calls to reduce them to preserve their efficacy. Due to these dual pressures on increased diseases and fewer antimicrobials, there is a global search for tools that can at least prevent diseases in poultry and cover both existing as well as emerging diseases. Vaccinations have, of course, contributed greatly to poultry health, but where they are unavailable or not yet commercially viable, all other options have to be explored with urgency.

The toolbox of poultry health

Vaccines are the standard tools, but what else is available to cover those diseases not preventable by them? In the discussion of health management, the view often stops after antimicrobials and possibly feed additives. However, all field experience shows that despite very promising peer-reviewed studies on a range of products, in practice, a much wider view is needed to maintain poultry health under today's production conditions. To have successful production, a range of products is typically considered to support health: immune modulators, butyrates, organic acids, phytogenics and, of course, probiotics. However, there is also clear evidence that those feed ingredients we have traditionally associated with performance more than health also benefit health, for example, proteases reducing substrate for potential pathobionts, toxin binders maintaining gut wall function and absorption enhancers providing the energy needed for optimal gut function. But it does not stop at the intestinal lining, diet formulation, processing, technology, how we house our birds and the frequently forgotten staff training in daily contact with the flocks. Only optimising all of these allows for healthy, well-performing flocks.

Probiotics – over 100 years of science

Especially after the AGP bans came in in countries across the globe, probiotics fast became a cornerstone of managing poultry health. After the long history of probiotic use in humans, poultry and livestock, microbiology has reached a point where one can begin to elucidate the complex modes of action. For the longest part of history, science understood microflora interactions to be mainly a competition of "good versus evil", and by adding more beneficial organisms, intestinal health would be assured. Today we understand while there is direct interaction of probiotics versus pathogens (i.e. the anti-clostridial surfactin production of bacillus sp. PB6),* interactions are much more complex than that. The science of probiotics is developing rapidly from quorum quenching, over microbiome-wide effects to very specific siderophore activities. Understanding the mechanisms is especially important when using multi-strain probiotics to ensure the strains are at minimum compatible and ideally synergistic with a range of modes of action between them.

What functions are needed from probiotics

The needs of the flocks determine the functions needed from probiotics. So today, in addition to controlling the gram+ clostridia, probiotics should now also address gram- Enterobacteriaceae such as Salmonella and E. coli. Typically, probiotic strains show their best efficacy towards a limited range of potential pathogens. Therefore, multi-strain probiotics are becoming more widespread to address a wider range of potential pathogens.

Ideally, those strains should modulate potential pathogens by direct inhibition*. This is possible for some probiotic strains and can even be demonstrated in-vivo. However, a very effective reduction of pathogens also has the risk of selection for resistance or tolerance in the pathogens*. Therefore, additional effects, such as reducing pathogenicity or promoting beneficial groups for health and intestinal function, are desirable. Even more complex functions are being explored, for example, reducing the pathogens' ability to invade intestinal cells.

Into the poultry feed

While microbiology is evolving rapidly, the challenges of keeping a probiotic alive through feed milling remain the same. Any probiotic candidate strain has to be able to withstand processing conditions (heat and moisture) and be fully compatible with standard additives like organic acids, coccidiostats or minerals. It also has to be stable when mixed with the feed or premix matrix. This can also be observed in commercial probiotics, with only a few lactobacillus-based probiotics remaining and virtually all new probiotics originating from spore-forming species, even though spore forming alone is no guarantee for processing stability but requires additional confirmation of its stability.

In-vitro modes of action

Direct inhibition of potential pathogens can be demonstrated in-vitro. It is a well-proven approach by using optical density measurements of potential pathogens to screen many probiotic candidates because of the high numbers of potential pathogens from field and lab. As interactions can be very strain-specific both for the probiotic and pathogen strain, this is a good approach to verify that a probiotic can work across regional pathogens, not just collection strains.

However, more than inhibition, other modes of action against pathogens can be explored in- vitro as well. For example, some probiotic strains can reduce the invasiveness of Salmonella sp. This can be evaluated in-vitro with Salmonella carrying a gene construct that can measure both rpsM and hilA expression in the presence of probiotic candidate strains or their supernatants*. hilA is associated with the invasiveness of Salmonella. A down-regulation, therefore, makes Salmonella less likely to be able to colonise outside the chicken intestine.

In-vivo modes of action

With more emphasis on the microbiome and quorum sensing as modes of action today, early in-vivo trials have become indispensable in selecting new probiotics alongside laboratory screenings. In a recent study at the University of Vienna/Austria, 100 male broiler chicks were challenged on days 14,16 and 18 with an APEC (avian pathogenic) E. coli strain at 5*10⁸ CFU. Treatment groups include a control with and without E. coli, respectively, two doses of a specific multi-strain probiotic and a commercially available probiotic with claims for E. coli management. The results showed that the multi-strain probiotic could significantly reduce E. coli in the caecum compared to both control and the other commercial probiotic.

Result

Figure 2 The level of E. coli in the caecum after challenge with APEC

Conclusions