The investigators compared sources of antibiotic resistant genes in human, animal, soil, water/sediment, and wastewater treatment plants.
Investigators from University of Gothenburg in Sweden in order to determine where initial mobilization events of ARGs may occur. While it has long been hypothesized that these ARGs originated in environmental bacteria, the study authors wrote, there have been increasing efforts to identify their exact origins.
The investigators used 22 origin species that had been previously identified in order to quantify presence of these species in different environments. They determined that these species were mainly found in wastewaters and human stool, and the 2496 unique samples they collected corresponded to 5 main categories: human, animal, soil, water/sediment, and wastewater treatment plans.
Proteobacteria dominated the wastewater treatment plants and water/sediments categories, the study authors observed. Most of the soil environments contained Actinobacteria or Proteobacteria, they added, while the human- and animal-related environments were made up of a mix of Firmicutes, Bacteroidetes and Actinobacteria.
The wastewater treatment plants polluted with urban waste had the highest relative abundance of origin species, the study authors said. Furthermore, almost all of the origin species were present in the majority of all samples from the wastewater treatment plants, with few exceptions.
There were environments in which the abundance of origin species varied considerably between samples, the study authors said, but they found that human stool samples taken from subjects treated with antibiotics (81%) demonstrated a significantly higher abundance of Enterobacter mori compared to the subjects not treated with antibiotics (303%). However, no origin species seemed to be significantly more abundant in human stool than in any other environment. These species (except for Shewanella algae) were significantly more likely to be detected among wastewater treatment plant samples compared to stool samples.
“In order to fight antibiotic resistance we cannot focus only on preventing the spread of those types of resistant bacteria that are already in circulation, we also need to prevent or delay the emergence of new ones,” lead author Fanny Berglund said in a press release.
The study authors wrote that occurrence of the origin species in a small proportion of humans or a relatively low abundance compared to the wastewater environments likely is a contributing factor to a lower probability for mobilization and transfer of the corresponding ARG to pathogens. It doesn’t rule out the possibility that the human microbiome was the site of mobilization, though.
To manage novel threats from problematic species and ARGs, the study authors suggest more efforts are put in practice to understand the species, mechanism, drivers, and environments involved in resistance gene mobilization.
“There is a lot of focus on reducing antibiotic use in humans and animals,” Berglund continued in the statement. “This is of course important, but our study show that we also need to pay attention to our waste streams, as this seems to be a place where new variants of antibiotic resistance could emerge.”