Bacterial-derived antimicrobials as potential alternatives for antibiotic-free broiler production

Authors: Zhang, Liya
Advisor: Fliss, Ismaïl
Abstract: For decades, antibiotics have been used in the poultry industry, not only for the prevention and treatment of bacterial infections, but also for promoting animal growth. However, a selective pressure by overuse and misuse of antibiotics contributes to the development of antibiotic resistance, posing a rising global public health threat. Therefore, antibiotic-free broiler chicken production is becoming increasingly popular worldwide due to consumers' demand and there is need to develop potential alternatives to antibiotics for use in the poultry sector. Numerous challenges need to be overcome in producing antibiotic-free broilers. Many studies have been carried out to look for natural agents with beneficial effects. The general objective of this thesis is to investigate the potential of bacterial-derived antimicrobials, namely reuterin, microcin J25 and lactic acid as alternatives to antibiotics for use in the broiler chicken industry. The first specific objective was to isolate and characterize Lactobacillus reuteri strains from the intestinal tract of broiler chickens. A total of 800 bacterial strains were isolated from broilers and screened for reuterin-producing ability. Three strains, namely L. reuteri C1-8, L. reuteri C1-14 and L. reuteri C1-18 were identified and shown to display a wide range of inhibitory spectrum. L. reuteri C1-14 exhibited the highest inhibitory activity after 1 h of anaerobic fermentation in a glycerol solution. All three L. reuteri survived simulated stomach and intestinal juice conditions. L. reuteri C1-14 showed susceptibilities to most clinically important antibiotics. Based on all criteria considered, L. reuteri C1-14 was selected as the most promising strain to be used as a probiotic in the poultry industry. For the second specific objective of this thesis, different bacterial-derived antimicrobial compounds, namely reuterin, microcin J25 and lactic acid, were evaluated alone or in combination, for their antimicrobial activity. Using the microdilution checkerboard assay, the combinations reuterin + lactic acid and reuterin + microcin J25 showed a synergic effect, making these compounds effective at concentrations 4 times lower than that used alone. Sprayed onto chilled chicken carcasses, reuterin + lactic acid mixture reduced Salmonella spp. counts by 2.02 Log CFU/g, whereas reuterin + microcin J25 and peracetic acid induced 0.83 and 1.13 Log CFU/g reductions, respectively. Applied as a post-chill spray, these mixtures could contribute to improve the food safety of poultry products by decreasing Salmonella counts on chicken carcasses. In the third specific objective, the efficacy of two synergetic consortia containing reuterin (5 mM) and lactic acid (0.78% v/v) or microcin J25 (0.08 µM) on microbiota and sensory attributes of raw chicken legs were evaluated. Based on total viable counts, the combination of reuterin and lactic acid or microcin J25 slowed down the growth of spoilage microbiota, thereby extending the shelf life of 2 to 3 days. Significant drops in sensory quality (including odor, color and overall appearance) occurred in the nontreated group, while slight changes occurred in the consortia groups over the same period. Reuterin combined with lactic acid or microcin J25 seems to provide a promising approach to control the growth of spoilage microorganisms on chicken meat. Finally, the last specific objective was dedicated to the evaluation of the effects of reuterin + microcin J25 and L. reuteri in drinking water on growth performance, intestinal microbiota and microbial metabolite profiles in broiler chickens. The results showed that birds received antibiotic and 5 mM reuterin + 0.08 µM microcin J25 exhibited greater body weight gain (about 6.19% and 4.56%, respectively) than negative control treatment (P < 0.05), while supplementing L. reuteri did not significantly affect broiler growth performance. The influence on the overall structure of bacterial communities by reuterin + microcin J25 was similar to antibiotic treatment. For microbial metabolites, supplementation with reuterin + microcin J25 positively affected the short chain fatty acids concentrations in the caeca than did the control groups. In summary, these results provide evidence that supplementation with reuterin + microcin J25 can likely improve the intestinal environment by changing microbial composition and metabolites, which had a positive effect on the growth performance and great potential as an efficient antibiotic alternative for broiler chicken production.
Document Type: Thèse de doctorat
Issue Date: 2021
Open Access Date: 9 August 2021
Grantor: Université Laval
Collection:Thèses et mémoires

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