When livestock manure is used on agricultural land, there is also increasing concern about antibiotic residues and antibiotic resistance genes that may end up in the environment with the manure, in addition to the known attention to environmental problems. In this project we investigate the influence of manure with antibiotic residues and resistance genes on the agricultural soil on which this manure is spread and on the crops that are then grown on it.
We take and analyze samples of manure of different animal origin as well as from the agricultural soil before and after fertilization. We also work with leeks and carrots that we grow under experimental controlled conditions on fertilized soil that we inoculate with relevant antibiotic concentrations. We analyze the samples to quantify the antibiotic residues, to investigate the (antibiotic-resistant) bacterial shifts (via both outplacement and 16S metabarcoding) and to quantify antibiotic resistance genes (via both qPCR and whole plasmidome sequencing). Conjugation experiments are also conducted to gain insight into the diversity of the resistance genes that are actually transferred with strains that are relevant for soil or vegetables. Finally, we draw up a quantitative exposure analysis model to estimate the risk of human exposure to antibiotic resistance genes and residues via the consumption of vegetables.
It is estimated that 700,000 people worldwide die annually as a result of antibiotic-resistant bacteria. The problem therefore has a serious health and economic cost. In addition to the human sector, the animal sector is also responsible for a large proportion of antibiotic use. This is expected to increase sharply in the future due to the growing world population and the rising demand for meat. The direct link between the animal sector and people has already been studied, namely the transfer of antibiotic residues, resistance genes and pathogens via the consumption of meat. In the meantime it has been shown that the indirect route via the environment may play an equally important role: manure from animals treated with antibiotics ends up on agricultural soil, as a result of which antibiotic residues and resistance genes also end up in the soil, on and in plants, in watercourses, etc. come. In Belgium, a country with intensive livestock farming and associated high antibiotic use and intensive arable farming, there is still little information about this risk.