In feed Bacitracin alters turkey microbiota functional and antibiotic resistance genes in a dose dependent manner

Authors: OLADELE, PAUL - Purdue University; WICKWARE, CARMEN - Oak Ridge Institute For Science And Education (ORISE); Trachsel, Julian; Looft, Torey; JOHNSON, TIMOTHY - Purdue University

Submitted to: Conference Research Workers Disease Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 12/6/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: OBJECTIVES: Bacitracin methylene disalicylate (BMD) is an in-feed antibiotic used to improve feed efficiency (subtherapeutic dose) or to treat disease (therapeutic dose) in poultry production. While antibiotic administration can improve animal health or production, it may increase antibiotic resistant bacteria. Thus, the impact of in-feed antibiotics is important to understand to gauge risk, but also identify pathways to target for maintaining animal health with non-antibiotic interventions. METHODS: We investigated the longitudinal effects of feeding subtherapeutic (50g/ton of feed) or therapeutic (200g/ton) BMD on intestinal metagenomes of commercial turkeys. Two-hundred and forty poults were randomly divided into three treatment groups (no antibiotic control, subtherapeutic BMD and therapeutic BMD). The therapeutic BMD group received 200g/ton BMD for 35 days, followed by 50g/ton until day 78. Ten turkeys from each treatment group were euthanized 7, 35 and 78 days after BMD administration began. The cecal content of the euthanized birds were collected for metagenomic analysis. DNA was sequenced on an Illumina HiSeq3000 and PacBio RSII SMRT sequencing technology for short and long reads, respectively. Sequence assemblies were generated with metaSPAdes and open reading frames were predicted with metagenemark. Annotations were created with CARD RGI for antibiotic resistant genes (ARG) and TIGRfam database for metabolic functional genes. RESULTS: Both doses of BMD reduced numbers of unique open-reading frames and there was a decrease in the number of genes involved in metabolism after early BMD exposure. The therapeutic dose of BMD increased antibiotic resistance genes, conjugation-related genes belonging to type IV secretion system, as well as transduction-related genes. The effect of BMD was transient in the subtherapeutic dose while the effect was observed until day 78 in the therapeutic dose. Estimated bacterial growth rate was reduced in the therapeutic dose on day 7, but restored by day 35, while tryptophan synthesis from chorismate increased in a dose dependent manner between days 7 - 35. Overall, the effect of subtherapeutic BMD on the turkey cecal microbiota was temporary while that of therapeutic dose was lasting. These metagenomic results are in general agreement with earlier metabolome analysis, indicating that metabolomic shifts are likely due to changes in the microbiota rather than a change in nutrient metabolism and absorption by the host. CONCLUSIONS: These results show that although microbial metabolism was altered soon after BMD administration, there was recovery in the subtherapeutic dose (relative to non-medicated) with distinct metabolic functions in the therapeutic dose. The dose-dependent selection for antibiotic resistance genes is important to inform veterinary practices and risk evaluations of in-feed antibiotics used in turkey production. Identifying mechanisms of action for in-feed antibiotics may also lead to viable alternatives to antibiotics to support animal agriculture.