Romanian scientists have recovered a bacterial strain from approximately 5,000-year-old ice inside a Transylvanian cave, and laboratory testing shows it resists 10 modern antibiotics spanning multiple drug classes. The organism, formally designated Psychrobacter sp. SC65A.3, was never exposed to pharmaceutical compounds, which means its resistance toolkit evolved naturally over millennia, long before humans began mass-producing antibiotics. That distinction matters because it challenges the common assumption that drug resistance is primarily a modern, hospital-driven crisis and opens a window into how bacteria armed themselves against chemical threats in the ancient world.
The work, led by researchers from Babeș-Bolyai University and their collaborators, adds a new line of evidence to the idea that resistance is an ancient survival strategy rather than a purely human-made problem. As an explainer in The Conversation notes, bacteria in natural environments have long competed with antibiotic-producing microbes such as fungi, forcing them to evolve sophisticated defence mechanisms. Psychrobacter sp. SC65A.3 offers a rare, time-stamped glimpse of those defences as they existed thousands of years before modern medicine, preserved in ice that acted as both a physical and ecological archive.
A 25-Meter Ice Core and the Microbe Inside It
A team of Romanian scientists drilled a 25.33-meter ice core from Scarisoara Ice Cave, a site in Romania’s Apuseni Mountains that holds one of the largest underground ice blocks in the world, estimated at roughly 100,000 cubic meters and more than 10,000 years old according to research published in Scientific Reports. Within the deeper strata of that core, researchers isolated Psychrobacter sp. SC65A.3 from layers radiocarbon-dated to approximately 5,000 years before present. The bacterium belongs to a genus commonly found in cold environments, from polar seas to refrigerated food, but this particular strain had been locked in ice since the Bronze Age, sealed away from any contact with synthetic drugs or modern agriculture.
Scarisoara is no stranger to microbiological investigation. Earlier studies documented bacterial and archaeal communities across ice layers spanning up to approximately 13,000 years, covering strata from recent deposits through layers roughly 400, 900, and 4,000 to 5,000 years old. A previous coring campaign in 2003 recovered a roughly 22.5-meter core, establishing the site’s value for paleoclimate and paleobiology research. What sets the new study apart is its focus on a single living isolate rather than community-level DNA surveys, enabling direct testing of how the organism behaves when confronted with drugs it has never encountered.
Resistant to 10 Drugs Without Ever Seeing a Pharmacy
Phenotypic antibiotic susceptibility testing, published in Frontiers in Microbiology, showed that Psychrobacter sp. SC65A.3 resists 10 antibiotics across multiple classes. The researchers grew the bacterium in controlled conditions and exposed it to panels of drugs that include categories commonly used in clinical medicine, such as beta-lactams and aminoglycosides. The strain survived concentrations that would kill or inhibit typical susceptible bacteria, earning it a profile that, on paper, resembles that of a modern multidrug-resistant pathogen. Yet this organism predates the discovery of penicillin by roughly five millennia.
The finding supports a growing body of evidence that antibiotic resistance genes are ancient features of microbial life, not recent mutations driven by hospital overuse alone. Soil bacteria, cave microbes, and permafrost organisms have all been shown to carry resistance determinants that predate the antibiotic era. What makes SC65A.3 notable is the breadth of its resistance, spanning 10 agents, combined with its confirmed isolation from precisely dated ancient ice rather than from environmental samples where contamination timelines are harder to pin down. The study’s authors sequenced the organism’s complete chromosome, deposited in GenBank under accession CP106752.1, providing a public record that other labs can mine for resistance gene architecture and mobile genetic element analysis.
How Scientists Confirmed the Strain’s Identity
Taxonomic identification relied on sequencing the 16S ribosomal RNA gene, a standard molecular barcode for bacteria. The partial sequence is publicly available under GenBank accession MN577402.1, allowing independent researchers to run similarity searches against thousands of known Psychrobacter isolates. That step preceded whole-genome sequencing and confirmed the organism belongs to the Psychrobacter genus before the team invested in deeper genomic analysis. The genome assembly, cataloged as RefSeq assembly GCF_025642195.1, gives the scientific community a standardized package for downloading annotation files and replicating the resistance gene scan.
This layered identification pipeline matters because claims about ancient organisms are only as strong as the contamination controls and taxonomic rigor behind them. By depositing both the 16S marker and the full chromosome in public databases, the Romanian team invites scrutiny, an important signal of confidence in the data. Still, one limitation deserves attention: the study focuses on phenotypic resistance, meaning it documents what the bacterium survives rather than fully mapping which specific genes confer each resistance trait or whether those genes sit on mobile elements capable of jumping to other species. That distinction is important because mobile resistance genes pose a far greater public health threat than chromosomal ones that stay put.
Why Ancient Resistance Genes Matter for Modern Medicine
Antimicrobial resistance is not an abstract laboratory concern. In the European Union and European Economic Area alone, resistant infections cause more than 35,000 deaths annually, according to surveillance data from the European Centre for Disease Prevention and Control. Understanding how resistance evolves in the absence of pharmaceutical pressure could reshape drug development strategy. If bacteria can develop broad resistance simply through ecological competition with fungi and other microbes, then new antibiotics designed without accounting for those ancient mechanisms may fail faster than expected once they enter clinical use.
Psychrobacter sp. SC65A.3 also underscores that resistance traits can be stable over geological timescales. The genes and regulatory systems that allowed this strain to withstand multiple drug classes appear to have persisted through thousands of years of dormancy in ice. That stability suggests resistance determinants may be deeply embedded in bacterial genomes as core survival tools, ready to be reactivated when conditions demand. For modern medicine, this means that even if hospitals and farms drastically cut antibiotic use, environmental reservoirs of resistance will continue to seed microbial populations with ancient solutions to chemical threats, complicating efforts to roll back the tide of superbugs.
From Cave Ice to Global Research Agendas
Although SC65A.3 itself is not a known human pathogen, its genome offers a template for understanding how non-pathogenic environmental bacteria can act as genetic banks for resistance traits that might one day move into disease-causing species. Researchers can now scan its chromosome for efflux pumps, enzyme families, and membrane modifications that blunt antibiotic action, then look for related sequences in clinical isolates. Discussions on platforms such as the Frontiers community forum highlight how comparative genomics across environmental and hospital strains can reveal whether similar resistance modules are already circulating in pathogens or poised to jump via horizontal gene transfer.
The Scarisoara findings also feed into a broader push to treat caves, permafrost, and other long-lived archives as libraries of microbial evolution. By sampling different depths and ages, scientists can reconstruct how resistance repertoires changed as climate, vegetation, and atmospheric chemistry shifted over thousands of years. That historical perspective may help policymakers and drug developers distinguish between resistance patterns that are truly new, driven by modern antibiotic use, and those that simply reflect the re-emergence of ancient capabilities. In turn, future therapies might aim not only to outpace bacterial evolution but also to anticipate strategies that microbes have already tested and refined across deep time.
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*This article was researched with the help of AI, with human editors creating the final content.
