Hidden for decades, hospital superbug built resistance in waves, peaking in the mid‑2000s Sadie Harley Scientific Editor Robert Egan Senior Editor Decades-old hospital samples have helped University of East Anglia (UEA) researchers uncover how a deadly antibiotic-resistant "superbug" quietly tightened its grip across the globe. It lurked in hospital corridors for decades, largely unnoticed by the wider public. But now an international team—including scientists at the Quadram Institute and in Canada and Mexico—have uncovered how one of the world's most feared superbugs rose to global dominance.

In a groundbreaking new study, researchers pieced together the genetic history of Acinetobacter baumannii—a notoriously stubborn hospital pathogen—using samples stretching back as far as the 1970s. They found that this bacterium evolved and adapted quietly for decades, accumulating small changes that eventually made it resistant to antibiotics. The study, "New isolates from the 1970s to early 2000s provide insights into the evolution of Acinetobacter baumannii international clone 2 and its resistome," was published in the journal Microbial Genomics.

Lead researcher Dr. Benjamin Evans, from UEA's Norwich Medical School, said, "We know that bacteria that cause infections in people can adapt to the antibiotics we use to treat them, rendering the antibiotics ineffective. "We looked at a specific type of bacterium called Acinetobacter baumannii from the 1970s to the present day.

"This bacterium particularly thrives in hospital environments and can cause infections that are extremely difficult to treat—particularly for vulnerable patients. "Understanding how it evolved into such a formidable threat is really important in stopping its spread. But until now, the genetic events behind this bacterium's success were poorly understood.

"What we found is that it has adapted in waves, with each wave producing bacteria that were better adapted to resist antibiotics than the previous wave. "Our work provides one of the clearest pictures yet of how antibiotic resistance can accumulate gradually—and then suddenly tip the balance in favor of the pathogen. "One thing is clear—this superbug didn't just appear.

It was decades in the making, and it's still evolving." How the research happened Scientists made the breakthrough by combining decades-old bacterial samples with cutting-edge genome sequencing. The team assembled a unique collection of 226 Acinetobacter baumannii samples dating from the 1970s to the early 2000s. These historical samples were carefully grown in the lab before their DNA was extracted, purified and sequenced using long-read Oxford Nanopore technology.

To build a global picture, the newly sequenced genomes were merged with more than 1,000 more recent genomes from six continents. Using high-performance computing, the scientists compared all 1,281 chromosomes and created a detailed evolutionary tree. They paired this analysis with a comprehensive scan of antimicrobial resistance genes, tracking how these genes appeared, disappeared and reshaped the bacteria over time.

Tracking a drug-resistant threat By aligning genetic changes with sample dates and locations, the team identified when key resistance traits emerged and how they spread globally.