TDK conference 2024

One of the defining perspectives of our time in veterinary and public health is the One Health concept, which is closely linked to the widespread dissemination of antimicrobial resistance. The use of antibiotics through feed or drinking water is particularly significant, as the resulting selective pressure not only alters the composition of the gut microbiome but also its antimicrobial resistance gene pool.

Our aim was to investigate the effect of amoxicillin, authorized for use in chickens, administered at a reduced dose (1/4x) and at a therapeutic dose (1x), under conventional conditions, on the weight gain of the animals, the composition of the gut microbiome, and the antimicrobial resistance gene pool.

From day 14, the treatments resulted in significantly better weight gain compared to the negative control group. In terms of gut microbiome composition, the Bacillota phylum was dominant in all cases, followed by the Pseudomonadota phylum, with no significant changes at the phylum level due to the treatments. However, at the family level, we observed that with age, the Lactobacillaceae family became predominant, and at this level, the treatments led to significant compositional changes. The 1/4x amoxicillin dose resulted in the dominance of the Turibacteriaceae family, while the 1x amoxicillin dose led to an overrepresentation of the Enterobacteriaceae family.

A total of 781 antimicrobial resistance genes were identified before treatment, which decreased to 637 after treatment. Significant changes in resistance mechanisms against different antibiotic classes were also observed after treatment, except in the negative control group. Among the extended-spectrum beta-lactamase genes, we detected the presence of a CTX-M-1 gene after the 1/4x amoxicillin treatment, while the TEM-1 and TEM-135 genes were found in similar proportions before and after the treatments. The proportion of plasmid-borne genes, as well as mobile genetic elements, showed a significant decrease after the 1/4x amoxicillin treatment.

In summary, our findings indicate that the dose of amoxicillin significantly influences the composition of the antimicrobial resistance gene pool, which is likely linked to the selective pressure exerted by the antibiotic on the gut microbiome. In the future, it would be worthwhile to include additional active substances in similar studies, as the results obtained may contribute to a more comprehensive understanding of the spread of antimicrobial resistance.