Staphylococcus aureus is a type of bacteria commonly found on the skin and in the nose of healthy individuals. While it's usually harmless, it can sometimes cause infections, ranging from mild skin infections to more serious issues like pneumonia and bloodstream infections. Some strains of Staphylococcus aureus are resistant to antibiotics, which can make treatment challenging. It's important to practice good hygiene to prevent the spread of this bacterium.