What are the alternatives? While the debate rages over what is driving the seemingly inexorable rise of antibiotic-resistant microbes, alternatives to antibiotics and products capable of reducing the risk of antibiotic resistance transfer through the food chain are clearly required. Of the functional ingredients currently in use for microbial control, yeast mannan-rich fractions (MRF) are widely used in animal nutrition and have been shown to improve animal performance in a manner similar to antibiotic-like growth promoters. Given their ability to bind and limit the colonisation of gut pathogens, MRF have proven to be an effective solution for pathogen control, as well as supporting overall health and performance. While the early use of yeast mannan products was linked with control of pathogens such as Salmonella and E. coli, recent studies have shown that MRF supplementation of poultry diets can significantly enhance the diversity of the intestinal microflora and in doing so, decrease the prevalence of microbial pathogens. In terms of developing strategies to reduce or limit the use of antibiotics, perhaps an elegant solution is to find ways to make the therapeutics more effective. MRF supplementation of the diets of broilers has been associated with a decrease in selected antibiotic resistance gene copy number. This is potentially linked to the ability of MRF to reduce plasmid transfer between microbes (Figure 1), and in doing so, prevent the spread of antimicrobial resistance. As part of ongoing efforts to support restriction and non-therapeutic use of antimicrobials in the poultry and pig industries, recent research at Alltech has focused on the mechanisms surrounding antimicrobial resistance and its impacts on antimicrobial efficacy toward common pathogens, such as resistant E. coli. Newly published research from the team at the Alltech European Bioscience Centre in Dunboyne, Ireland, has shown that MRF can influence bacterial metabolism, and in doing so, influence the sensitivity of resistant bacteria to antibiotics. This new research demonstrates that when resistant E. coli is grown in the presence of MRF, its growth and metabolism are altered, resulting in antimicrobial-resistant strains becoming increasingly sensitive to antibiotic treatment (Figure 2). The use of MRF in this instance has been shown to enhance the sensitivity of bacteria to the effects of antibiotics, and in doing so, potentially reduce the minimum inhibitory concentration (MIC) required.
The future of antibiotics From a production standpoint, it is essential that any moves toward antibiotic-free production systems improve overall feed quality, as animals that are fed quality feeds are less susceptible to enteric problems. Ultimately, this move from least-cost feed formulation and reliance on antibiotics will be toward high-quality feeds containing functional ingredients.
Figure 2 - MRF modulates growth of susceptible and resistant E. coli. Growth curves of (a) antibiotic-susceptible E. coli. and (b) antibiotic-resistant E. coli supplemented and not supplemented with MRF (0.5%) in the presence and absence of ampicillin (AMP).
Glucose 0.5% MRF only 0.6 0.5 0.4 0.3 0.2 0.1 0 0 a –0.1 Glucose 0.5% MRF only 0.6 0.5 0.4 0.3 0.2 0.1 0 0 b –0.1 200 400
600 Time (mins)
800 1000 1200 No MRF/No Antibiotic 200 400
600 Time (mins)
800 1000 1200 No MRF/No Antibiotic 0.01µg/mL AMP 0.01µg/mL AMP + 0.5% MRF 0.5µg/mL AMP 0.05µg/mL AMP + 0.5% MRF
0.05µg/mL AMP 0.05µg/mL AMP + 0.5% MRF
50µg/mL AMP 50µg/mL AMP + 0.5% MRF
Conclusions Concerns about antibiotic resistance among scientists, regulators and consumers have driven the EU ban on AGPs and been a catalyst for change in the U.S. This has heralded a global move to reduce antibiotic usage, and further ongoing changes in animal production systems are likely to be substantial. Ultimately, what is required are innovative replacement products and alternative strategies. The use of functional feed components, such as MRF, represents one such innovative approach to break the cycle of resistance.
▶ ANTIBIOTIC REDUCTION | DECEMBER 2021 23
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