How does antimicrobial resistance spread from gut bacteria to potentially dangerous hospital superbugs? Antimicrobial resistance (AMR) is a growing global health threat, driving increased patient mortality, prolonged hospital stays and rising healthcare costs. “Our findings show that not all resistance plasmids, even when they belong to the same category, behave the same way,” commented Gan. “Some plasmids are evolutionarily adapted to the mammalian gut, where they can quietly and efficiently spread antibiotic resistance. Under oxygen-poor conditions similar to those in the intestine, the capsule became less viscous, allowing resistance plasmids to transfer more easily, which is a contrast to results seen under standard oxygen-rich laboratory conditions.