Climate-related warming and droughts could encourage bacteria to share resistance genes
Climate change could increase hard-to-treat bacterial infections, two studies suggest.
Heat increased resistance to antibiotics in bacteria found in artificially warmed prairie soils, researchers report April 22 Nature. And as drought robs the soil of moisture, antibiotics in the environment concentrate in what little water remains, encourage the growth of resistant microbesreported another team in April Natural microbiology.
Both studies highlight that heat and drought caused by climate change are the forces driving an increase in antibiotic resistance in natural environments, which in turn could threaten human health.
Antibiotic resistance has been known for a long time linked to human misuse or overuse. The risk arises when patients discontinue treatment or when doctors mistakenly prescribe medications to treat viral infections that antibiotics cannot cure. But “we often forget or even neglect the historical fact that these clinical drugs are not only found in CVS pharmacies,” says Xiaoyu Shan, a microbial ecologist at Caltech.
Many antibiotics come from soil microbes, which use these compounds as weapons to interfere with their competitors. While drug developers have exploited these compounds to treat various bacterial infections, resistance to specific antibiotics can give microbes a survival advantage, both in the environment and in the human body.
Climate change could also increase antibiotic resistance. Previous studies have shown that higher temperatures are associated with an increase in antibiotic-resistant infections. “But we really don’t know the mechanism,” says Jizhong “Joe” Zhou, a microbial ecologist at the University of Oklahoma in Norman.
For a decade, from 2009 to 2020, Zhou and his colleagues artificially heated grassland plots to 3 degrees Celsius above ambient air temperature using infrared lamps. Genetic analyzes of soil samples showed that the abundance of antibiotic resistance genes was about 25 percent higher among microbial communities in heated soils than in normal plots.
Warming went hand in hand with this increase, the team found. As bacteria have adapted to thrive in warmer soils, antibiotic resistance has also developed. And other bacteria that could handle the heat – some of which were already resistant to antibiotics – had a head start. It is possible that bacteria exchange genes with each other helped this resistance spread throughout the microbial community. Overall, the results suggest that soil microbes become resistant over time, not because of exposure to an antibiotic, Zhou says, but because of warming itself.
Meanwhile, diminishing water sources encourage resistance through exposure, Shan and colleagues found. Data collected from croplands and grasslands in California, a forest in Switzerland, and a wetland in China revealed that soil microbes produce more antibiotics during a drought than under normal conditions. Laboratory experiments have shown that antibiotics concentrate in drier soils. The concentrated compounds kill susceptible bacteria, allowing resistant strains to develop.
It’s a bit like making rock candy. “You put sugar in a solution, and if you start to evaporate the solution, it will concentrate the sugar to the point where you start making rock candy,” says study co-author Dianne Newman, a bacterial physiologist at Caltech. (Newman is a board member of the Society for Science, a nonprofit educational organization in Washington, D.C., which publishes Scientific news.)
Drying soils doesn’t produce “candy,” but it does force antibiotics and microbes to inhabit smaller spaces. This proximity can help antibiotics kill susceptible bacteria, while other microbes become resistant through the exchange of genes with their neighbors. These resistant strains could be transmitted to humans. Using data from hospitals in 116 countries, the team found higher frequencies of antibiotic-resistant infections in drier places.
It’s difficult to directly connect what’s happening in the soil to the clinic, says epidemiologist and economist Ramanan Laxminarayan of the One Health Trust in Washington, D.C., who was not involved in either study. Indeed, other factors could also explain why drier regions tend to have greater antibiotic resistance, such as the lack of health facilities in rural deserts, which can delay care.
Arid environments tend to be dusty, says Shan. Windblown dirt could carry microbes across the landscape and expose people to antibiotic-resistant pathogens.
Still, both studies highlight the importance of paying attention to the world around us, Laxminarayan says. “We are at the mercy of the environment. It’s not like we can solve all the public health problems just by working within hospitals. We will have to look at the environment as well.”
