Increased levels of multi-drug resistant bacteria worldwide pose a significant threat to human and animal health. The recommendations in the WHO’s global action plan were to phase out and research alternatives to using antibiotics in animal farming. This study aims to identify natural plant supplements that can be used in animal feeds as sustainable alternatives to conventional antibiotics to promote animal health and performance.
Plant extracts from traditional Chinese medicine were screened and their antibacterial activity was demonstrated against Campylobacter jejuni, Listeria monocytogenes, Escherichia coli and Salmonella enterica subsp. enterica serovar Enteritidis. Agrimonia pilosa Ledeb, Smilax glabra Roxb, Anemone chinensis Bunge, and Iris domestica (L.) Goldblatt and Mabb were found to exhibit strong broad-spectrum antibacterial activity against the above pathogens. A. pilosa Ledeb demonstrated antibacterial activity comparable to erythromycin and ampicillin. The synergistic antibacterial activity of combinations of these plant extracts and with antibiotics was also investigated against the above pathogens. Only one combination of extracts of A. chinensis Bunge and A. pilosa Ledeb indicated potential synergistic effects against both C. jejuni and E. coli. Combinations of A. chinensis Bunge and S. glabra Roxb, and A. pilosa Ledeb and S. glabra Roxb also indicated potential synergistic effects against E. coli. A. pilosa Ledeb, A. chinensis Bunge and S. glabra Roxb extracts each in combination with ampicillin and erythromycin indicated additive effects against C. jejuni, L. monocytogenes, E. coli, and S. enteritidis. In vitro assays were used to examine the bactericidal activity of A. pilosa Ledeb, S. glabra Roxb, A. chinensis Bunge, and I. domestica (L.) Goldblatt and Mabb over 24 hours in broth and in selective broth with chicken caecum content. The findings showed A. pilosa Ledeb, A. chinensis Bunge, S. glabra Roxb reduced caecum colonisation of E. coli, L. monocytogenes, and S. enteritidis in vitro within 0.5 hours. The results indicated a significant reduction of ≥99.9% of the above pathogens and rapid bactericidal activity comparable to ampicillin (P <0.001).
The final part of this study investigated the effect of plant supplementation to broiler chicken diets on their performance, nutrient digestibility, and gastrointestinal tract microbiota. The results of the poultry trial highlighted the selective antibacterial activity of S. glabra Roxb, which decreased pathogenic bacteria, E. coli and Campylobacter spp. on day 21 (P <0.05) and 35 (P <0.01) and increased lactic acid bacteria relative abundance compared to the antibiotic group on day 14 (P <0.001) and 35 (P <0.01). In addition, S. glabra Roxb, and A. chinensis Bunge significantly increased weight gain compared to the negative control and the positive control receiving the recommended nutrient specification diet (P <0.001) and this was comparable to the positive amoxicillin control group. A. pilosa Ledeb, A. chinensis Bunge, and S. glabra Roxb significantly decreased feed conversion ratios compared to the negative control group and had comparable feed conversion ratios to the positive amoxicillin control group (P <0.001).
The study contributes to addressing gaps in the research literature on the use of plant extracts as potential alternatives to antibiotics in poultry farming. It provides additional information on the antibacterial activity of many plant extracts against pathogens commonly found in the poultry gastrointestinal tract and new information about others including A. pilosa Ledeb, S. glabra Roxb, A. chinensis Bunge, and I. domestica (L.) Goldblatt and Mabb. The results of the poultry trial also indicate the potential of S. glabra Roxb and A. chinensis Bunge in reducing pathogens, enhancing the bird’s beneficial microbiota, and improving bird performance. Overall, the findings of this study highlight the potential of using plant extracts as a supplement to poultry diets.
|Date of Award||Jul 2021|
- Queen's University Belfast
|Sponsors||Department of Agriculture, Environment and Rural Affairs|
|Supervisor||Elisabeth Ball (Supervisor), Michael Tunney (Supervisor) & Chen Situ (Supervisor)|