The atmosphere is a large-scale dissemination route for bacteria carrying antibiotic resistance genes. A research team from Université Laval and Université Clermont Auvergne has shown that these genes can be carried by clouds.
“This is the first study to show that clouds harbor antibiotic resistance genes of bacterial origin in concentrations comparable to other natural environments,” says Florent Rossi, first author of the study and a postdoctoral fellow in the team of Caroline Duchaine, professor of Laval University. Faculty of Sciences and Engineering and researcher at the Heart and Lung Institute of Quebec-Université Laval.
To observe this phenomenon, the team sampled the clouds at the summit of the Puy de Dôme, a dormant volcano in France’s Massif Central. At an atmospheric research station located 1,465 meters above the ground, scientists conducted 12 cloud sampling sessions over two years using high flow rate “voids.”
Analysis of these samples revealed that they contained about 8,000 bacteria per milliliter of cloud water, on average. “These bacteria usually live on the surface of vegetation or soil. They are aerosolized by the wind or by human activity, and some of them rise to the atmosphere and participate in the formation of clouds”, explains Florent Rossi. The concentrations are variable: they range from 330 to more than 30,000 bacteria per milliliter of cloud water. Between 5% and 50% of these bacteria could be alive and potentially active.
various sources
Using all their data, the scientists measured the concentration of 29 subtypes of antibiotic resistance genes found in atmospheric air masses. The clouds contained, on average, 20,800 copies of antibiotic resistance genes per milliliter of cloud water.
“Oceanic clouds and continental clouds each have their signature of antibiotic resistance genes. For example, continental clouds contain more genes for resistance to antibiotics used in animal production,” explains Florent Rossi.
Although the airborne transport of antibiotic resistance genes is a natural phenomenon, the widespread use of antibiotics in agriculture and medicine has contributed to the proliferation of these resistant strains and their spread in the environment.
“Our study shows that clouds are an important pathway for antibiotic resistance genes to spread over short and long distances. Ideally, we would like to localize emission sources resulting from human activities to limit the spread of these genes.” .
The health effect of the spread of these antibiotic-resistant genes will be something to investigate in future research.
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