Gram-positive bacteria are a group of bacteria that have a thick cell wall made primarily of peptidoglycan. This structure allows them to retain a purple dye during a laboratory staining process known as the Gram stain, which is used to classify bacteria. They are typically spherical (cocci) or rod-shaped (bacilli) and can be found in various environments, including soil, water, and as part of the human microbiome. These bacteria are important in many fields, including medicine and food production. Some Gram-positive bacteria, like Staphylococcus aureus, can cause infections, while others, such as Lactobacillus, are beneficial and used in the production of yogurt and other fermented foods.