Clouds can spread antibiotic-resistant bacteria, Canadian-French study finds

The spread of antibiotic resistant bacteria poses a major threat to global health and food security as the use of antibiotics continue to grow. And now, a team of researchers from Quebec and France say bacteria with antibiotic-resistant genes can even spread through the clouds.

The study, published last month in the journal Science of The Total Environment, looked at samples taken from clouds at the Puy de Dôme summit, located 1,465 metres above the ground atop a dormant volcano in central France.

Analysis of the samples found anywhere between 330 to over 30,000 bacteria per millilitre of cloud water, with the average being around 8,000.

“This is the first study to show that clouds harbour antibiotic resistance genes of bacterial origin in concentrations comparable to other natural environments,” lead author Florent Rossi of the Université Laval said in a news release. “These bacteria usually live on the surface of vegetation or soil. They are aerosolized by the wind or by human activities, and some of them rise into the atmosphere and participate in the formation of clouds.”

The researchers measured the concentration of 29 subtypes of antibiotic-resistant genes and found the clouds had an average of 20,800 copies of these genes per millilitre of cloud water.

“Oceanic clouds and continental clouds each have their signature of antibiotic resistance genes. For example, continental clouds contain more antibiotic resistance genes used in animal production,” Rossi said.

Antibiotic resistance can occur when bacteria are exposed to antibiotics and develop immunity to these drugs, especially as the use of antibiotics continues to grow in health care and agriculture.

The World Health Organization says the growth of antibiotic-resistant bacteria has made it more difficult to treat a growing list of bacterial infections, such as pneumonia, tuberculosis and foodborne disease — leading to longer hospital stays, higher medical costs and increased mortality.

“Our study shows that clouds are an important pathway for antibiotic-resistance genes spreading over short and long ranges. Ideally, we would like to locate emission sources resulting from human activities to limit the dispersal of these genes,” Rossi said.