Feed additives


Controlling pathogens with selected yeast fractions

The overuse and misuse of antimicrobials in humans and livestock has led to an increase in antibiotic resistance to certain bacteria. Yeast pro- and postbiotics could provide the means to reduce the use of antibiotics within the livestock industry as they have positive effect on animal resilience and performance.

Foodborne pathogenic illnesses kill 420,000 people a year according to the World Health Organization (WHO). This death toll is headed by diarrhoeal diseases which are responsible for more than half the total loss of life in cases linked to the consumption of contaminated foods. The O‘Neill review (2015) forecasts that if we continue using antibiotics in the same way as before, deaths due to antimicrobial resistance will reach 10 million in 2050. WHO and OIE have developed a global action plan, seeking alternatives to the use of antibiotics in an attempt to avoid a future where there is a lack of treatments for bacterial diseases (World Health Organisation, 2016). Yeast probiotics and yeast fractions (YF) are seen as efficient solutions to help reduce the use of antibiotics in livestock, thanks to their proven positive effects on animal resilience and zootechnical performance.

In vivo studies : Proven effects of yeast fractions on pathogen control

Bacterial pathogens present different mechanisms in the process of colonisation and invasion. When colonising, bacteria adhere to the host cell surface. One of the best-known mechanisms is pili, which allows bacteria to sustain binding activity while passaging through the gastrointestinal tract. Pili displays an adherence factor which explains its binding efficiency. Pathogens with mannose-binding fimbriae recognise the mannoproteins present in yeast fractions, which are similar to the surface of intestinal epithelial cells. Hence, the ingestion of yeast fractions might provide competitive attachment sites for host receptors, thus reducing the risk of pathogenic bacteria colonising the intestinal tract and removing them from the intestine. Supplementing animal feed with yeast fractions is being shown to decrease pathogen pressures in the gut, while promoting pathogen removal from animals by preventing the first steps of infection (namely pathogen attachment to intestinal cells).

Recent peer reviewed scientific articles have demonstrated that adding Safmannan (SYF), a premium quality selected yeast fraction, to animal diets can help enhance resilience against several important bacterial diseases, especially the ones caused by E. coli, Salmonella or Clostridium perfringens. Adding SYF to animals’ diet has been proven to promote the animals’ natural defences and zootechnical performance, while also reducing mortalities.

In vitro test : Efficient method to disclose what’s behind

There is a need to understand what happens in animal’s gut when yeast fractions are added to feed, and the modes of action that allow yeast fractions to diminish pathogen load. For this purpose, several methods have been developed.

Posadas et al., 2017, revealed an adhesion between SYF and several pathogens (E. coli O157:H7, Clostridium difficile, Clostridium perfringens, and different serovars of Salmonella). A qualitative method, which involved scanning electronic microscopy, was used to illustrate adhesion (Figure 1). This clearly showed the binding of pathogens to premium quality SYF. It was also revealed that not all bacteria bind at the same level. Results showed that SYF could bind Salmonella Typhimurium at a rate of up to 98%; Salmonella Typhi, up to 59%; and C. perfringens, up to 75%.

Figure 1 – SEM image of Salmonella enterica Typhimurium bound to SYF.

Controlling pathogens with selected yeast fractions

2 recent publications, Santovito et al., 2019a and 2019b, revealed that not all yeast fractions bind pathogens in the same way, with some binding according to their composition and 3D structure. To defend this hypothesis, researchers focused on Clostridium perfringens (C. perfringens), performing adsorption tests by the isotherm method (Figure 2). This showed the effect of SYF was dose-dependent, achieving 2 logs reduction (cfu/mL) using 1,25mg/mL of product. Furthermore, the presence of SYF was shown to have an effect on the inhibition of the growth of C. perfringens. SYF can therefore increase lag phase duration, significantly reducing maximum growth rates and final cell count, compared to control results. Based on this data, it was concluded that SYF has an effect on binding C. perfringens and that, moreover, it can block vital metabolism in the bacterium due to the absorption of the bacterial surface.

Figure 2 – Effect of contact time on adsorption rate of Clostridium perfringens by SYF.

Controlling pathogens with selected yeast fractions


Pathogen load within live animals, of course, can be influenced by their prior exposure to contamination, their basic health and any stress factors they’ve encountered, some of which may have led to increased microbial shedding. Combatting such issues, in order to reduce contamination risks for consumers, needs to embrace a range of activities, such as establishing better animal health, reduced stress and the reduction of pathogen levels in faeces.

At a time when society is seeking to reduce the use of antibiotics, other solutions should be examined to avoid increasing bacterial infections. Premium quality SYF was screened via numerous in vitro and in vivo R&D and field studies, in different species including poultry, aquaculture, ruminants and companion animals. These different tests have shown consistent positive effects of SYF on pathogen pressure reduction, gut function optimisation, natural defences enhancement and the overall improvement of animals performance.

References are available upon request

Nuria VIECO, PhD, Microbiology R&D manager, Phileo by Lesaffre.