Impact of antibiotics of anthropogenic origin on bacterial soil communities in agricultural ecosystems. Review

Abstract

Soil is considered to be the most diverse microbiological ecosystem on Earth. Microbial soil biodiversity is substantially influenced by animal husbandry, intensive agricultural practices and soil cultivation (tillage, crop rotation, irrigation, organic and inorganic fertilization, application of pesticides etc.). Soil mismanagement represents a worldwide topic that impairs natural ecosystem sustainability as a first consequence. In order to understand and correctly apply soil management practices a deep insight in ecological processes is necessary. Soil microbiota have a great impact on both natural processes (biogeochemical cycles) as well as various other aspects that could influence human health and the quality of life (micro- or macro-contaminants, pharmaceuticals, fertilizers, phytosanitary products). Pharmaceuticals, especially antibiotics are intensively used in animal husbandry either as therapeutic agents or for prophylactic measures. Antibiotics of microbial, semi-synthetic or synthetic origin impact the metabolism of bacteria: at subinhibitory concentrations they act as hormetic intercellular messengers stimulating gene expression. Higher amounts have bacteriostatic or bactericidal effects according to their mode of action. Both result in a profound modulation of bacterial community structure and biodiversity by boosting genotypic and phenotypic variability and induction of antibiotic resistance. They also pose an indirect effect on the communities (generating different genotypic and phenotypic variability such as antibiotic resistance). Agricultural management practices like application of organic fertilizers (e.g. manure) expose soil microbiota to a variety of hazardous agents of anthropogenic origin including antibiotics, antibiotic resistant bacteria and antibiotic resistance genes which interact with the indigenous soil resistome. This paper describes the impact of human land-use, especially the ecological effects of antibiotics on natural ecosystems and the increase of antibiotic resistance in soil communities.