Just about everyone by now knows (in theory) how to solve the increasingly dire problem of antibiotic-resistant diseases: Medical professionals should be more judicious on when exactly to prescribe antibiotics; patients should only take their antibiotics as prescribed; and the factory farms using and abusing antibiotics on their slums of livestock should maybe rethink their approach to animal welfare.
This common advice may seem deceptively simple, but it could be obscuring an unexpectedly significant factor driving the global rise of superbug bacteria. That’s according to a sweeping new study in The Lancet Planetary Health that analyzed more than 480,000 Salmonella genomes collected from 139 countries between 1940 and 2023.
Researchers with the Chinese Academy of Sciences in Beijing, Cambridge, and Oxford in the U.K., and their international partners say that decades of increasing hothouse temperatures have helped to serve as an incubator, boosting Salmonella’s (and likely other bacteria’s) antimicrobial resistance (AMR).
The past eight decades of Earth’s warming climate were strongly linked to a 10% increase in the quantity of Salmonella strains found with antimicrobial resistance genes (ARGs) worldwide, the study finds. And the association was recorded in 82 of the 100 countries that the researchers focused on to examine more local effects.
The problem appears to be getting worse. The findings imply that the warming caused by climate change may be responsible for roughly one quarter of the 38% increase in antibiotic-resistant Salmonella genes observed since 2010, as compared to the years between 1940 and 2010. And the trend was more pronounced in hotter regions of the world like Latin America, the Caribbean, and parts of Asia and the Pacific, which tended to “exceed the global average.”
Bugging out
The researchers tested the measured rise in Salmonella ARGs against “counterfactual scenarios” informed, in part, by those “pronounced regional disparities” that they documented in hotter parts of the world.
Changes in precipitation, they noted, had a perversely nonlinear impact on the evolution of Salmonella superbugs, with “elevated ARG levels at both extremes of the precipitation spectrum.”
On one end, the researchers wrote, “unprecedented flooding events have been shown to accelerate ARG spread across aquatic ecosystems,” as have “urban floodwaters” via the crowded area’s “compromised wastewater infrastructure.” But, simultaneously, they found, “drought-induced low water levels can concentrate antibiotic residues and antimicrobial-resistant bacteria in compromised water supplies, potentially amplifying AMR transmission events.”
The result was that among the 82% of nations that displayed these stronger Salmonella ARGs, the clearest and most distinct link between rising superbugs and the local impact of climate change was documented in both arid-hot and wet-hot regions of the world like the Middle East, North Africa, South Asia, and Sub-Saharan Africa.
The study’s authors turned to a form of regression analysis called Tobit modeling to help them carefully analyze their massive dataset of 488,232 genomes of Salmonella strains sourced from the U.S. National Center for Biotechnology Information (NCBI). The method has been most widely used in cases like this, where censored data or other gaps introduce a mathematically tricky amount of zero values which can throw off statistical averages.
One worrying observation that the team uncovered through various iterations of their regression and Tobit models was a “significantly” positive relationship between insecticide use and rising Salmonella superbugs. The team theorized that overuse of these chemicals had a similar effect to over-prescribed or misused antibiotics, creating a “selective pressure that promotes the survival and proliferation of antimicrobial-resistant bacteria, similar to therapeutics.”
A feature and a bug
One key finding solidified the team’s suspicion that climate change plays a role in creating antibiotic-resistant Salmonella genes. The proliferation of Salmonella ARGs ramped up alongside the increased pace of rising temperatures from 2010 to 2023.
“This pronounced upward trajectory was observed across most geographical regions when compared with the baseline levels before 2010,” the team noted, “indicating a widespread escalation in AMR acquisition among Salmonella strains worldwide.”
The researchers hope their work (which included predictably dire extrapolations into the year 2100) will compel governments to better integrate their carbon-cutting goals with “enhanced antimicrobial stewardship” and the United Nations’ One Health surveillance program.
“Collectively, these findings highlight the importance of mitigating climate change as a strategic intervention to curb the spread of ARGs and, ultimately, to combat the global challenge of antibiotic resistance,” the team wrote.
