Asked by: Dave Cullis, Leicester
Salt kills some types of bacteria, effectively by sucking water out of them. In a process known as osmosis, water passes out of a bacterium so as to balance salt concentrations on each side of its cell membrane. Without water, bacterial proteins such as enzymes cannot function and eventually the cell collapses in on itself.
Some bacteria can tolerate salt; they are halotolerant. Certain strains of Staphylococcus, responsible for infections, blood poisoning, and even death, are halotolerant. These pathogens have a salt alert system that uses sponge-like molecules to prevent water loss.
Dr Emma Davies is a science writer and editor with a PhD in food chemistry from the University of Leeds. She writes about all aspects of chemistry, from food and the environment to toxicology and regulatory science.