Microbiologists have decoded the genome of the bacterium Psychrobacter sp. SC65A.3, which was isolated from an ice mass approximately 5,000 years old in Romania’s Scărișoara Cave. Research has shown that this microorganism is resistant to eight classes of modern antibiotics. These findings confirm that complex mechanisms of drug resistance evolved in nature long before the advent of medicine and human influence.

Ice Caves as Reservoirs of Ancient Genes

Arctic ice and permafrost have long been recognized as repositories of ancient microorganisms, but ice caves remain relatively unexplored. Extreme natural environments are considered natural reservoirs of resistomes—the collections of genes responsible for antibiotic resistance. Studying the evolution of these genes in isolated conditions is crucial for predicting how drug resistance may spread in today’s world.

Characteristics of the Isolated Strain

The SC65A.3 strain was obtained from an ice core extracted at a depth of over 25 meters. To determine the species and functions of the bacterium, researchers performed whole-genome sequencing. They also studied the physiological limits of the microorganism’s survival at different temperatures and salt concentrations. Additionally, the strain’s sensitivity to 28 antibiotics was tested, and its ability to inhibit the growth of 20 different pathogens was assessed.

Analysis revealed that the bacterium belongs to the species P. cryohalolentis, remains active at temperatures from +4 °C to +15 °C, and can tolerate high salt concentrations—up to 1.9 moles per liter of sodium chloride, about three times higher than the average concentration in the world’s oceans. The genome contains more than 100 resistance genes, including mcr-1, which is associated with resistance to colistin, an antibiotic of last resort.

Resistance and Antimicrobial Potential

The strain demonstrated resistance to 10 antibiotics from eight different classes, including third-generation cephalosporins, fluoroquinolones, and rifampicin. At the same time, the bacterium exhibited antimicrobial potential by suppressing the growth of 14 pathogens, including methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa.

Significance of the Research

The results show that ice caves serve as hidden reservoirs of ancient resistomes and bioactive compounds. Mechanisms of multidrug resistance have been developing in microbial communities for thousands of years, long before the clinical use of antibiotics. Studying such “preserved” systems provides access to unique enzymes and molecules that could form the basis for developing new antibacterial drugs.