A warmer planet might make deadly bacteria more resistant to antibiotics

Rising global temperatures are making it more difficult to combat bacteria with antibiotics.
Scanning electron micrograph of Escherichia coli
E. coli bacteria. NIAID

Tom Patterson became ill in 2015 while vacationing in Egypt. He was felled by Acinetobacter baumannii, an often deadly bacterium resistant to every antibiotic his doctors tried. Patterson, a University of California San Diego psychiatry professor, should have died, but didn’t. (Experimental infusions of bacteria-killing viruses known as bacteriophages ultimately saved his life.) But his near-death experience from a superbug he picked up in a warm country — an organism that also has afflicted many hospitalized wounded troops in Iraq and Kuwait — raises provocative questions about drug-resistant bacteria and their relationship to our increasingly hotter planet. “Travelers returning from tropical and other warm areas where multi-drug resistant pathogens have become more widespread will increasingly challenge the antibiotics on our shelves,” said Robert T. Schooley, an infectious diseases specialist at UC San Diego, who treated Patterson. “Turning up the temperature of the incubator in which we live will clearly speed the evolutionary clock of bacterial and other pathogens with which we must co-exist.” Experts already know that climate change has become a significant threat to global public health, particularly as rising temperatures have produced greater populations of disease-transmitting insects, such as mosquitoes. But warmth also encourages bacteria to grow, providing them a chance to mutate and elude drugs that once easily killed them. While antibiotic resistance is believed largely due to the indiscriminate prescribing of antibiotics, experts now think that other environmental stresses — climate change among them — also may be at work.

The world is confronting a growing and frightening danger from multi-drug-resistant infections, with many now difficult or impossible to treat. The World Health Organization has described this scenario as “one of the biggest threats to global health, food security, and development today.” There are more than two million cases and 23,000 deaths from antibiotic-resistant infections annually in the United States, according to the Centers for Disease Control and Prevention.

A recent study published in Nature Climate Change suggests that a link between climate change and bacterial resistance exists right here in the United States, particularly in its southern regions. Epidemiologists from Boston Children’s Hospital and the University of Toronto found that higher local temperatures and population densities correlated to a greater level of antibiotic resistance among a number of common bacterial strains.

a map
A representation of antibiotic resistance caused by climate change. Fawn Gracey/Boston Children’s Hospital

“Most work to date on the effects of climate on infectious diseases have focused on vector-borne and diarrheal diseases,” said Derek MacFadden, a research fellow at Boston Children’s Hospital and the study’s lead author. “However, our work suggests that climate may have an impact on antibiotic resistance in bacteria. If this is the case, then our expectations on how the burden of antibiotic resistance will change over time would need to consider climate — and may be underestimates.”

For their study, the researchers assembled a large database of U.S. antibiotic resistance information related to E. coli, K. pneumoniae, and S. aureus from a variety of sources, including hospital, laboratory and disease surveillance collected between 2013 and 2015. Their database totaled more than 1.6 million bacteria from 602 records in 223 facilities and 41 states — samples all isolated from people with resistant infections.

They then compared their data to latitude coordinates, as well as to mean and median local temperatures, and found that higher local average minimum temperatures correlated the most with antibiotic resistance. Local average minimum temperature increases of 10 degrees Celsius were linked to surges of 4.2, 2.2, and 3.6 percent in resistant strains of E. coli, K. pneumoniae, and S. aureus respectively, according to the study.

Finally, they also found that an increase of 10,000 people per square mile was related to 3 and 6 percent respective increases in resistance in E. coli and K. pneumoniae, indicating that population density also likely plays a role.

“Population growth and increases in temperature and antibiotic resistance are three phenomena that we know are currently happening on our planet,” said Mauricio Santillana, the study’s co-senior author and faculty member at Boston Children’s computational health informatics program. “But until now, hypotheses about how these phenomena relate to each other have been sparse. We need to continue bringing multidisciplinary teams together to study antibiotic resistance in comparison to the backdrop of population and environmental changes.”

a graph of rising temperatures
The rising global surface temperature shows an increase of approximately 1.4°F since the early 20th century. NOAA

The study also found higher rates of antibiotic prescriptions across geographic regions in areas with increases in bacterial resistance.

While the study suggests the brunt of problem is occurring in the South, MacFadden warned that no part of the country was safe. “If temperature is playing a role, then the effects could be felt everywhere, typically in regions with the greatest potential changes in temperature over time as you move toward the poles,” he said.

UC San Diego’s Schooley — who was not involved in the study — said any number of biological factors likely are involved. “With warmer temperatures, environmental populations of bacteria might increase in size, the horizontal transmission of bacterial resistance genes might increase, and interactions with animal populations — from a health perspective — might also evolve,” he said.

Still, he added: “A 10-degree change in minimum temperature is a relatively big change in climate since they are talking about a 6-degree change in mean global temperature by the end of the century. Nonetheless, this is yet more food for thought about why those who trivialize the potential impact of climate change are putting the planet at risk.”

The study authors called for additional research. “We have found associations, and more work is needed to identify the consistency of these findings across regions and possible mechanisms,” MacFadden said.

John Brownstein, the other senior co-author and director of Boston Children’s computational epidemiology group, pointed out that public health estimates already predict a perilous escalation in antibiotic resistance in the coming years. “But with our findings that climate change could be compounding — and accelerating — an increase in antibiotic resistance, the future prospects could be significantly worse than previously thought,” he said.

Marlene Cimons writes for Nexus Media, a syndicated newswire covering climate, energy, policy, art and culture.