People with hardened arteries have fewer of certain types of bacteria in their blood than healthy people — and this difference is too big to be just random chance.

Scientists found 11 types of bacteria in the blood that weren’t known to be linked to heart disease or gum problems—and these bacteria were much more or less common in people with early signs of clogged heart arteries than in healthy people.

People with severe calcium buildup in their heart arteries tend to have less of a specific bacteria called Fusobacterium nucleatum in their blood than people with healthy arteries.