A bacterial strain discovered frozen in an underground cave is resistant to 10 antibiotics, which could give scientists clues on preventing the rise of antimicrobial resistance.

Bacteria have evolved to adapt to Earth’s most extreme conditions, from scorching heat to temperatures well below zero. Ice caves host a variety of micro-organisms representing a source of genetic diversity that has not yet been studied extensively.

Researchers have carried out antibiotic resistance tests on bacteria found inside a 5,000-year-old layer of ice in the Scarisoara ice cave in Romania.

“The Psychrobacter SC65A.3 bacterial strain isolated from Scarisoara ice cave, despite its ancient origin, shows resistance to multiple modern antibiotics and carries over 100 resistance-related genes,” said Cristina Purcarea, a senior scientist at the Institute of Biology Bucharest. “But it can also inhibit the growth of several major antibiotic-resistant ‘superbugs’ and showed important enzymatic activities with important biotechnological potential.”

The team drilled a 25-metre ice core from the area of the cave known as the Great Hall, representing a 13,000-year timeline. To avoid contamination, ice fragments taken from the core were placed in sterile bags and kept frozen on their way back to the lab. There, the researchers isolated various bacterial strains and sequenced their genome to determine which genes allowed the strain to survive in low temperatures and which conferred antimicrobial resistance and activity.

They tested for resistance of the SC65A.3 strain against 28 antibiotics from 10 classes that are routinely reserved for treating bacterial infections, including antibiotics that have previously been identified as possessing resistance genes or mutations. 

“The 10 antibiotics we found resistance to are widely used in oral and injectable therapies used to treat a range of serious bacterial infections in clinical practice,” Purcarea said. Diseases such as tuberculosis, colitis and UTIs can be treated with some of the antibiotics that the researchers also found resistance to, including rifampicin, vancomycin and ciprofloxacin.”

SC65A.3 is the first Psychrobacter strain for which resistance to certain antibiotics – including trimethoprim, clindamycin and metronidazole – was found. SC65A.3’s resistance profile suggests that strains capable of surviving in cold environments could act as reservoirs of resistance genes, which are specific DNA sequences that help them survive exposure to drugs.

“If melting ice releases these microbes, these genes could spread to modern bacteria, adding to the global challenge of antibiotic resistance,” Purcarea said. “On the other hand, they produce unique enzymes and antimicrobial compounds that could inspire new antibiotics, industrial enzymes and other biotechnological innovations.”

Analysis of the genome also revealed 11 genes that are potentially able to kill or stop the growth of other bacteria, fungi and viruses. This has significant potential in a world where antibiotic resistance is a growing concern, the researchers said.