Why can’t unicellular organisms live in hot water?

Single-celled organisms are fairly simple. Most of them live in liquids. When heated, they die. This is due to too high a temperature. Temperature breaks down the proteins inside the cell. This causes the cessation of the body’s vital activity. But not all unicellular organisms die in hot water. Some microorganisms remain alive even in boiling water for some time. Therefore, when boiling water and milk, you need to keep the liquid on fire for some time so that all dangerous microorganisms die.