For years, researchers have been tracking a particularly nasty family of superbugs called CREs, or carbapenem-resistant Enterobacteriaceae, which can thwart antibiotics in our last lines of defense. Researchers have watched in horror as clinical isolates gathered new molecular weaponry, spread through medical facilities across the globe, and started causing more and more life-threatening infections.

But a new study suggests we’re still only seeing a glimpse of what they’re up to.

In a genetic analysis of 122 CREs that popped up in four US hospitals, researchers discovered that isolates are far more diverse than expected, and some of them could disarm our toughest drugs using methods researchers had never even seen before. The hospitals—three in Boston and one in Irvine, California—had little overlap in their CRE collections. Within each hospital, there was a variety of CRE types, spanning several species, with a medley of genetic backgrounds and resistance genes.