Biology subjects

Looft, T.

Publications and source records attributed to Looft, T..

2 recordsLinked to original sources

bioRxiv2025

In-feed bacitracin methylene disalicylate alters microbiota function and increases antibiotic resistance in a dose-dependent manner

Antibiotics are commonly used in turkey production to prevent and treat infection which can improve animal growth and efficiency, but the mechanism by which antibiotics improve animal performance, and the resistance risks associated with the antibiotic inclusion levels remain unclear, particularly in turkey production. Therefore, we investigated the longitudinal effect of subtherapeutic and therapeutic doses of bacitracin methylene disalicylate (BMD) on antibiotic resistance genes, mobile genetic elements, and metabolism genes by analyzing the turkey cecal metagenome. The therapeutic dose of BMD increased a vast array of antibiotic resistant genes (ARGs), conjugation-related genes of type IV secretion system and transduction-related genes for the length of the experiment (78 days), while a smaller, transient effect was observed due to the subtherapeutic dose. Estimated bacterial growth rate, estimated by metagenome assembled genome sequence coverage, decreased after 7 days of in-feed BMD, but increased in the therapeutic group over time. Tryptophan synthesis from chorismate increased in a dose-dependent manner between days 7 - 35. Overall, the effects of subtherapeutic BMD on the turkey cecal microbiota was temporary while those of a therapeutic dose were longer lasting. This study shows that antimicrobial resistance genes belonging to multiple antibiotic classes, and mobile genetic elements (MGEs) were increased after BMD administration. The enrichment these genes by BMD shows the risk associated with antimicrobial feed additives. BMDs effect on tryptophan synthesis provides a potential metabolic target for developing non-antibiotic microbiome modulatory growth promoters for turkey production. ImportanceAntibiotic use in agricultural animals remains a hotly debated and important topic to human, animal, and environmental health. The dose-dependent responses to BMD, an antibiotic fed additive allowed at both therapeutic and subtherapeutic doses, are not well understood. This study highlights that therapeutic use of BMD is a stronger selective pressure than the subtherapeutic dose for antibiotic resistance genes and genes related to horizontal gene transfer. This indicates that use of BMD could select for antibiotic resistant bacteria that may pose a risk to animal, human and environmental health. Additionally, this study highlighted that BMD decreased the activity of beneficially bacteria, and therefore may be associated with a decreased concentration of bacterial metabolites (especially tryptophan related) in the cecum. This may indicate that growth promoting antibiotics suppress bacterial activity generally, rather than allowing beneficial bacteria to generate beneficial metabolites.

microbiology↗

bioRxiv2021

Gene flux and acid-imposed selection are the main drivers of antimicrobial resistance in broiler chicks infected with Salmonella enterica serovar Heidelberg

Antimicrobial resistance (AR) spread is a worldwide health challenge, stemming in large part, from the ability of microbes to share their genetic material through horizontal gene transfer (HGT). Overuse and misuse of antibiotics in clinical settings and in food production have been linked to this increased prevalence and spread of AR. Consequently, public health and consumer concerns have resulted in a remarkable recent reduction in antibiotics used for food animal production. This is driven by the assumption that removing this selective pressure will favor the recovery of antibiotic susceptible taxa and will limit AR sharing through HGT, allowing the currently available antibiotic arsenal to be effective for a longer period. In this study we used broiler chicks raised antibiotic-free and Salmonella enterica serovar Heidelberg (SH), as a model food pathogen, to test this hypothesis. Our results show that neonatal broiler chicks challenged with an antibiotic susceptible SH strain and raised without antibiotics carried susceptible and multidrug resistance SH strains 14 days after challenge. SH infection perturbed the microbiota of broiler chicks and gavaged chicks acquired antibiotic resistant SH at a higher rate. We determined that the acquisition of a plasmid from commensal Escherichia coli population conferred multidrug resistance phenotype to SH recipients and carriage of this plasmid increased the fitness of SH under acidic selection pressure. These results suggest that HGT of AR shaped the evolution of SH and that antibiotic use reduction alone is insufficient to limit antibiotic resistance transfer from commensal bacteria to Salmonella. ImportanceThe reported increase in antibiotic resistant bacteria in humans have resulted in a major shift away from antibiotics use in food animal production. This has been driven by the assumption that removing antibiotics will select for antibiotic susceptible bacterial taxa, and this in turn will allow the currently available antibiotic arsenal to be more effective. This shift in practice has highlighted new questions that need to be answered to assess the effectiveness of antibiotic removal in reducing the spread of antibiotic resistance bacteria. This research demonstrates that antibiotic susceptible Salmonella Heidelberg strains can acquire multidrug resistance from commensal bacteria present in the gut of neonatal broiler chicks, even in the absence of antibiotic selection. We demonstrate that exposure to acidic pH drove the horizontal transfer of antimicrobial resistance plasmids and suggests that simply removing antibiotics from food-animal production might not be sufficient to limit the spread of antimicrobial resistance.

microbiology↗