By Stephen Beech
Bacteria frozen for thousands of years in an underground ice cave is resistant to 10 modern antibiotics, reveals new research.
Bacterial strains thriving in icy environments could worsen the global antibiotic resistance crisis – or play an “essential” role in solving it, say scientists.
They explained that bacteria have evolved to adapt to all of Earth’s most extreme conditions, from scorching heat to temperatures well below zero.
Ice caves are just one of the environments hosting a range of microorganisms that represent a source of genetic diversity that has not yet been studied extensively.
Scientists in Romania tested antibiotic resistance profiles of a bacterial strain that until recently was hidden in a 5,000-year-old layer of ice of an underground ice cave.
They found it could be an opportunity for developing new ways to prevent the rise of antibiotic resistance and study how resistance naturally evolves and spreads.
Study author Dr. Cristina Purcarea said: “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.
“But it can also inhibit the growth of several major antibiotic-resistant ‘superbugs’ and showed important enzymatic activities with important biotechnological potential.”
She explained that Psychrobacter SC65A.3 is a strain of the genus Psychrobacter, which are bacteria adapted to cold environments.
Some species can cause infections in both humans or animals.
Psychrobacter bacteria have biotechnological potential, but the antibiotic resistance profiles of the bacteria were largely unknown.
Dr. Purcarea said: “Studying microbes such as Psychrobacter SC65A.3 retrieved from millennia-old cave ice deposits reveals how antibiotic resistance evolved naturally in the environment, long before modern antibiotics were ever used.”
The research 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, the ice fragments taken from the core were placed in sterile bags and kept frozen on their way back to the lab.
The research team isolated various bacterial strains and sequenced their genome in the lab to determine which genes allow the strain to survive in low temperatures and which confer antimicrobial resistance and activity.
The researchers tested for resistance of the SC65A strain against 28 antibiotics from 10 classes that are routinely used to or reserved for treating bacterial infections.
The drugs tested included antibiotics that have previously been identified to possess resistance genes or mutations that give them the ability to resist drug effects.
That way, they could test whether predicted mechanisms translated into measurable resistance.
Dr. Cristina Purcarea, a senior scientist at the Institute of Biology, Bucharest, said: “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.”
Diseases such as tuberculosis (TB), colitis, and urinary tract infections (UTIs) can be treated with some of the antibiotics that the researchers 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.
Those antibiotics are used to treat UTIs, infections of lungs, skin, or blood, and the reproductive system.
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, according to the research team.
They say bacterial strains such as the one they examined hold both a threat and a promise.
Dr. Purcarea said: “If melting ice releases these microbes, these genes could spread to modern bacteria, adding to the global challenge of antibiotic resistance.
“On the other hand, they produce unique enzymes and antimicrobial compounds that could inspire new antibiotics, industrial enzymes, and other biotechnological innovations.”
In the Psychrobacter SC65A.3 genome, the researchers found almost 600 genes with unknown functions, suggesting a yet untapped source for discovering new biological mechanisms.
Analysis of the genome, published in the journal Frontiers in Microbiology, also revealed 11 genes that are potentially able to kill or stop the growth of other bacteria, fungi, and viruses.
Dr. Purcarea said such potential is becoming ever more important in a world where antibiotic resistance is a growing concern.
She says going back to ancient genomes and uncovering their potential highlights the important role the natural environment played in the spread and evolution of antibiotic resistance.
Dr. Purcarea added: “These ancient bacteria are essential for science and medicine, but careful handling and safety measures in the lab are essential to mitigate the risk of uncontrolled spread.”
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