Philip Mak's PhD Defence

Ecology of Antimicrobial Resistance and Investigation of Berry Pomace Alone or in Combination with a Lactobacillus Isolate as Alternatives to Antibiotics in Broiler Chickens

Antimicrobial use (AMU) in broiler production is highly regulated in many countries due to antimicrobial resistance (AMR) concerns, resulting in the use of alternative products including probiotics and phytochemicals. There are many studies that investigated the impacts of AMU on AMR in broilers, but there are limited studies evaluating how alternative produc-tion systems such as organic and raised without antibiotics (RWA) impact AMR. First study investigated AMR and gut mi-crobiota profiles of broilers raised in different feeding programs: conventional (CON), raised without medically important antibiotics (RWMIA), and raised without antibiotics (RWA). Antimicrobial-resistant Escherichia coli was prevalent in all three feeding programs, where sex-specific differences in AMR to ciprofloxacin, tetracycline, and gentamicin were ob-served. Gut microbiota analysis revealed significantly different cecal community diversities and bacterial taxa between feeding programs. Specifically, Enterococcus was more abundant in RWA compared to other programs, in which females abundance was higher than males. Second study evaluated the in-vitro characteristics of Lactobacillus reuteri isolated from broiler ceca for their probiotic potential. Lactic acid bacteria (LAB) strains were identified as L. salivarius, L. johnsonii, L. reuteri, and L. crispatus, where they demonstrated tolerance and stability in harsh conditions, autoaggregate, and bind to hydrophobic surfaces. Lactobacillus reuteri demonstrated the best probiotic characteristics, with low prevalence of antimicrobial resistance genes (ARGs) and no virulence genes. Reuterin (L. reuteri bacteriocin) exhibited antimicrobial activity against Gram-negative and Gram-positive bacteria and was stable while exposed to digestive enzymes and other harsh GIT conditions. The third study evaluated the in-vivo impacts of L. reuteri in broilers alone or in combination with cranberry and blueberry pomaces on anti-coccidial effects, growth performance, and AMR. Growth performance, body parameters, lesion scores, and oocyst counts revealed that broilers fed berry pomace in combination with L. reuteri showed potential in controlling coccidiosis while maintaining performance. Gut microbiota analysis revealed L. reuteri was more prevalent in market weight broilers fed the combination.
Date: August 4th 2023 at 9:00am