17 January 2023

Chinese scientists provide first global map of antibiotic resistance in soil


Researchers from Shanghai University described the global distribution of antibiotic-resistant genes in the soil. The phenomenon is especially evident in Europe, America and Asia. And is a threat to animal and human health

by Matteo Cavallito


Where in the world are antibiotic resistance genes in the soil? A team of Chinese scientists can finally tell. In a research published in the journal Science Advances, in fact, the authors, from the School of Geographic Sciences at East China Normal University in Shanghai, have compiled the first map on the distribution of this phenomenon, which has been recognized as a serious threat in recent decades.

“The massive use and misuse of antibiotics have resulted in the selective enrichment of antibiotic resistant genes (ARGs) in microorganisms in the environment, according to the research team,” writes the China Daily newspaper. “acquisition of ARGs by pathogenic bacteria would lead to problems in antibiotic treatment, posing a serious threat to the health of human beings and animals, according to the research team.”

The phenomenon is widespread in the Americas, Europe, and Asia

The spatial distribution of antibiotic-resistant genes in the Planet’s soils and the factors influencing their geographic presence are still unclear. Research therefore fills part of this gap by offering new insights into the subject. The researchers found, for example, that the presence of ARGs was significantly higher in agricultural soils when compared with land not used for cultivation or farming. The metagenomic investigation, conducted by sequencing 1,088 soil samples, revealed the presence of 558 different resistant genes.

Their highest concentration, the researchers explained, is found in certain areas characterized by high population density and strong crop and livestock industry development. These include “Western Europe, East Asia, South Asia and eastern United States.” In addition, the study “also illustrated a high normalized abundance of ARGs in comparatively high latitudes, such as northern Europe and New Zealand.”

Mercato degli antibiotici utilizzati principalmente per scopi zootecnici nei diversi paesi OCSE. FONTE: Antimicrobial Resistance, OECD 2016.

Antibiotic market (substances used primarily for livestock purposes) in different OECD countries. Source: Antimicrobial Resistance, OECD 2016.

The human factor

According to the researchers, the data collected leave no doubt: “These results, together with noticeable positive connections of ARGs with livestock and crop production, irrigation and manure, agriculture and pesticide, as well as barley and sheep production, provide convening evidence that elevated soil antibiotic resistance is primarily attributed to anthropogenic activities,” the research states.

“Further analysis,” China Daily writes, “revealed that human activities can increase the abundance of soil ARGs by introducing gut microbes and clinical pathogens into farmland via the use of agricultural sludge and manure.”

The dangers of antibiotic resistance

The issue is highly topical. In fact, the global veterinary-livestock sector still makes extensive use of antibiotics for various purposes, several researchers recall. These include animal growth, prophylaxis and disease treatment. However, the gut system of each animal is only able to absorb a portion of the administered dose. Which means that the remaining portion is excreted and thus spread into the soil. The use of manure as a soil conditioner can also be a problem.

The result is that crops end up absorbing antibiotic molecules, and bacteria that come into contact with them can quickly mutate and become resistant to these substances. Such resistance occurs in the soil, in the animal digestive system and in the human digestive system.

But there is more. As a study by the Department of Soil and Water Systems at the University of Idaho points out, antibiotic contamination alters the action of soil microorganisms and also reduces the soil’s ability to store carbon. The result is increased emissions that foster climate change.

Climatic factors

Climatic factors assume an important role in promoting the abundance of antibiotic-resistant genes in the soil. In fact, Chinese scientists have found a higher incidence of the phenomenon in places with lower temperatures and higher rainfall. “One feasible mechanism underlying such a result is that low temperature and high soil moisture restrict decomposition rate, causing the accumulation of soil organic matter that are hospitable for the growth and proliferation of microbes carrying ARGs,” the research states.

Finally, the study suggests some strategies to curb the spread of resistant genes in the soil following the so-called One Health approach that aims to protect human and environmental health. These include curbing antibiotic use on livestock farms, decoupling agricultural production from livestock management, reducing irrigation through untreated wastewater and excessive pesticide use, and improving sanitation infrastructure in the agricultural sector.