SuperbugsLow antibiotic levels in the environment may spur drug resistance
A new study is providing new evidence that low concentrations of antibiotics in the environment could be contributing to the evolution of antibiotic resistance. The researchers report that even when bacterial communities in wastewater are exposed to small amounts of the antibiotic cefotaxime, selection pressure for clinically important antibiotic-resistant genes occurs. Moreover, they also found that the selection pressure for resistance may be just as strong as when exposed to high concentrations of the drug.
A study by scientists in England and China is providing new evidence that low concentrations of antibiotics in the environment could be contributing to the evolution of antibiotic resistance.
In a study published in the journal mBio, researchers with the University of Exeter Medical School, the University of Hong Kong, and drug-maker AstraZeneca report that even when bacterial communities in wastewater are exposed to small amounts of the antibiotic cefotaxime, selection pressure for clinically important antibiotic-resistant genes occurs. Moreover, they also found that the selection pressure for resistance may be just as strong as when exposed to high concentrations of the drug.
CIDRAP says that the findings are important because they suggest that environments that are commonly found to have trace amounts of antibiotics, such as hospital effluent and rivers and streams that receive wastewater, could be an important, and overlooked, breeding ground for antibiotic-resistant bacteria
“The significance of this finding is that environments with very low antibiotic concentrations (eg, natural environments) may be just as important in selection for antibiotic resistance as environments with very high antibiotic concentrations (eg, hospitals, and in the human or animal gut during antibiotic therapy),” lead study author Aimee Murray, PhD, a research fellow at University of Exeter Medical School, said in an email to CIDRAP News.
Selection for an important resistance gene
In the study, Murray and her colleagues exposed raw, untreated wastewater from a sewage treatment plant to varying amounts of cefotaxime, a third-generation cephalosporin that’s used to treat a wide variety of infections and has been recognized by the World Health Organization as a critically important antibiotic.
“Wastewater can contain a cocktail of antibiotics and other chemicals which may select for antibiotic resistance,” Murray explained. “Therefore wastewater is ideal for studying the effects these antibiotics and chemicals may have on the very bacterial communities being exposed to them.”
The levels of cefotaxime ranged from the minimal selective concentration—a sub-inhibitory amount that’s just enough to select for resistance and is similar to antibiotic levels previously found in treated wastewater and surface waters—to levels used to treat clinical bacterial infections. While previous research has shown that resistance can occur when individual species of
