The Yangtze River in Shanghai, China. | Photo: leonidrad auf pixabay
Antibiotic resistance is an escalating global health concern, intensified by the pervasive presence of antibiotic resistance genes in natural environments. "Antibiotic resistance genes indicate that resistance to antibiotics is genetically anchored in microorganisms and that they can pass on this genetic information. There is evidence that some clinical antibiotic resistance genes originated in environmental organisms," said Prof. Hans-Peter Grossart. Microorganisms are increasingly developing antibiotic resistance in rivers, for example through the discharge of wastewater containing pharmaceuticals.
The Yangtze River is the third longest river in the world and one of the most important freshwater sources in China. It has different land use types along its banks. Therefore, different sections of the river are subjected to different anthropogenic disturbances. The research team collected a total of 204 samples from 37 sampling sites across approximately 6000 kilometers of the river, with each site including six different habitat types, namely free-living and particle-associated bacteria in the water, bacteria from surface and bottom sediments, and bank samples from the surface and deeper soil.
22 types of antibiotic resistance genes, mainly in aquatic bacteria
The results show that antibiotic resistance is widespread and diverse in the microbial communities of the Yangtze River, covering almost all antibiotic species: 22 types of antibiotic resistance genes (655 ARG subtypes) constituted the whole resistome of the six sampled riverine habitats. Resistance genes for bacitracin, macrolide-linkosamide streptogramins (MLS), sulfonamides, vancomycin and multiresistance formed the mayor part of the Yangtze River resistome. "Our results show a higher prevalence and diversity of antibiotic resistance genes in water-associated microorganisms compared to those in the other habitat types of the Yangtze River," said Hans-Peter Grossart. A remarkable pattern of coalescence of resistance was found within similar habitat types - the same combinations of resistance genes occurred frequently.
Risk index: How dangerous are the resistances for humans?
The researchers also developed a risk index. Using this index, they were able to demonstrate that macroorganisms from water habitats – free-living and particles-associated – contribute the most to human health risks and that the risk of antibiotic resistance genes increases, especially in particle-associated microorganisms, the more the river sections are used and polluted by humans. "This result is particularly relevant for drinking water abstraction from the Yangtze. There is a risk that ingested environmental bacteria will pass on resistance to microorganisms that are relevant to health," said Hans-Peter Grossart. "The results cannot be transferred 1:1 to other rivers, but they show the high risk of antibiotic resistance in freshwater ecosystem heavily impacted by humans."
