Single-celled microorganisms that don’t require living hosts. They come in many different shapes and thrive in diverse environments including extreme heat and cold. They live in soil, oceans, and the human gut. Bacteria are classified by the makeup of their cell walls and are identified by a Gram stain. Hence the term, a “Gram-positive,” or “Gram-negative” bacteria. Some bacteria share space and resources in our body and are beneficial to human health. Other bacteria cause infections and disease.
