IT IS cold, dark and very old inside the Scarisoara ice cave. Located deep in the Apuseni mountains of Romania, this subterranean cathedral houses a massive block of ice that has been slowly accumulating for over 10,000 years. As Cristina Purcarea and her team from the Institute of Biology Bucharest carefully hauled a 25-metre ice core up from the cave’s Great Hall, they weren’t just looking for climate data. They were looking for the “living dead”—bacteria trapped in a deep-freeze since the dawn of human civilisation.
What they found has unsettling implications for our future. Among the ice, the team identified a strain of Psychrobacterbacteria, dubbed SC65A.3, that has been dormant for 5000 years. Despite having no contact with humanity’s pharmaceutical arsenal, this ancient microbe is already resistant to 10 classes of modern antibiotics. “The PsychrobacterSC65A.3 bacterial strain, despite its ancient origin, shows resistance to multiple modern antibiotics,” says Purcarea.
The discovery shatters the comforting illusion that antibiotic resistance is a purely modern “lifestyle” disease of our own making. Instead, it seems the genetic blueprints for defeating our most powerful medicines—including vancomycin and ciprofloxacin—were circulating in the natural world long before we ever built a hospital. As the planet warms and ancient ice melts, these subterranean reservoirs of resistance could be on the move.
Psychrobacter are specialists of the cold. They are found in permafrost, Antarctic soils and the deep sea. To survive the crushing silence of the Scarisoara ice, SC65A.3 evolved a toolkit of over 100 resistance-related genes. While we view antibiotics as medicine, in the microbial world, they are often used as chemical weapons in a perpetual war for space and nutrients. “Studying microbes such as Psychrobacter SC65A.3 reveals how antibiotic resistance evolved naturally in the environment, long before modern antibiotics were ever used,” Purcarea says.
To test the strain’s mettle, the team exposed it to 28 different drugs. The results were startling. The bacteria shrugged off rifampicin, used to treat tuberculosis, and vancomycin, often considered a drug of last resort for serious “superbug” infections. For the first time in this genus, researchers also saw resistance to trimethoprim and metronidazole, common treatments for urinary tract and respiratory infections.
This is what microbiologists call the “natural resistome”—the vast, ancient library of resistance genes that exists in the wild. The danger is that these genes aren’t fixed in place. Bacteria are famously promiscuous, capable of swapping DNA like trading cards through a process called horizontal gene transfer. If melting ice releases these ancient specialists into modern ecosystems, they could pass their prehistoric secrets to contemporary pathogens. “If melting ice releases these microbes, these genes could spread to modern bacteria, adding to the global challenge,” warns Purcarea.
But the news from the ice isn’t entirely bleak. In the same way that a poisoner must also possess the antidote, SC65A.3 appears to be a prolific producer of its own antimicrobial compounds. The team discovered 11 genes in its genome that allow the bacteria to kill or inhibit the growth of rival “superbugs,” fungi and even viruses.
This dual nature makes the cave ice a double-edged sword. While it holds a potential threat, it is also a treasure trove for drug hunters. The genome of SC65A.3 contains nearly 600 genes with entirely unknown functions. These could be the blueprints for the next generation of antibiotics, or perhaps industrial enzymes capable of functioning at temperatures where modern chemistry stalls. “They produce unique enzymes and antimicrobial compounds that could inspire new antibiotics,” says Purcarea.
For now, the team is treating their discovery with extreme caution. The researchers are working under strict safety protocols to ensure their “time-travelling” bacteria don’t escape the laboratory. “Careful handling and safety measures in the lab are essential to mitigate the risk of uncontrolled spread,” Purcarea notes.
The story of SC65A.3 is a reminder that we are newcomers to a very old game. Our struggle against infection is just the latest chapter in a multi-billion-year chemical arms race. As we continue to probe the world’s shrinking ice, we are finding that the past is not as buried as we thought. The secrets frozen in the dark of Scarisoara may help us survive the “superbug” era—or they may simply show us that our enemies were ready for us thousands of years before we arrived.
Study link: https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2025.1713017/full
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