Antibiotic resistant bacteria can spread in an unexpected way — through clouds

Bacteria that are resistant to antibiotics can live on the surfaces of plants or within the soil, but they can also survive in clouds, meaning they can travel thousands of kilometres and potentially invade new environments, a recent study found. 

Researchers from Université Laval in Quebec and Université Clermont Auvergne in France showed, for the first time, that bacteria carrying antibiotic-resistant genes can be harboured and carried in the atmosphere.

“Considering that the atmosphere is a system that is pretty harsh for the bacteria, (the number they found) is quite a lot, actually,” said Florent Rossi, first author of the study and postdoctoral fellow at Université Laval’s Faculty of Science and Engineering.

Antimicrobial resistance genes are a naturally occurring phenomenon present everywhere in nature, he explained, adding the scientific community has known for a long time that these genes can exist in the air (which can be carried from the ground to the atmosphere by the wind).

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However, “what we didn’t know is how high they can be and how far they can travel. And the fact that we found them in clouds highlights that they can travel for long distances,” Rossi stated.

The rise of antibiotic-resistant bacteria has made it increasingly challenging to effectively treat a growing number of bacterial infections, including pneumonia, tuberculosis and foodborne illnesses. This trend has resulted in longer hospitalizations, higher medical expenses and elevated mortality rates, according to the World Health Organization (WHO).

Antibiotic resistance has become so prevalent that the WHO has classified it as one of the 10 global public health threats facing humanity.

Because of its prevalence in nature, Rossi and his team wanted to understand how far antibacterial resistance genes can travel.

The researchers of the study, which was published on March 20 in the Science of The Total Environment, sampled clouds at the Puy de Dôme summit, a dormant volcano in south-central France. Using an atmospheric research station 1,465 metres above ground, the scientists conducted 12 cloud sampling sessions over two years using high-flow rate “vacuums.”

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After reviewing these samples, the team found they contained about 8,000 bacteria per millilitre of cloud water, on average. Between five per cent and 50 per cent of these bacteria could be alive and potentially active, the study found.

It is unclear exactly how far the antibiotic-resistant genes can travel, but because clouds can be as far up as six kilometres into the sky, Rossi estimated they can spread “over thousands of kilometres.”

“We don’t know whether the bacteria in the atmosphere can grow when it lands in soil when it rains, and we don’t know if those bacteria can spread their antimicrobial resistance genes,” Rossi added.

Antibiotics are used for medicine, but mainly in agriculture to prevent disease and to improve growth production, according to a 2022 report by the Public Health Agency of Canada (PHAC). The agency estimated that in 2020, 82 per cent of all antibiotics used in Canada were related to livestock.

As the use of antibiotics increases, bacteria can develop resistance to one or more of them, explained Brian Conway, medical director of the Vancouver Infectious Disease Centre.

This problem can worsen if antibiotics are used inappropriately for extended periods of time. As a result, bacteria can evolve to become resistant to multiple antibiotics that are commonly used, he said.

An average of 26 per cent of bacterial infections are currently resistant to first-line antimicrobials, and because of that, resistant bacterial infections were responsible for the deaths of at least 14,000 people in Canada in 2018, a report by the Council of Canadian Academies stated.

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Because of the risk, Conway believes the Université Laval’s study is important in highlighting “another way in which these bacteria can spread from one location to another.”

“They are existing on the ground and they evaporate up into clouds. The clouds move, it rains, and then the bacteria are spread to that new location,” he said.

“Perhaps it teaches us that in places where there haven’t necessarily been cases of antibiotic-resistant bacteria that have spread from one person to another, this is a way in which they could be introduced into an environment.”

The study, he emphasized, highlights the importance of minimizing the emergence of antibiotic-resistant bacteria, which can be achieved by reducing the use of antibiotics in both medical and agricultural contexts.

— with files from Reuters