Mycobacteria are a group of bacteria known for their thick, waxy cell walls, which make them resistant to many common antibiotics. They are often found in soil and water and can cause diseases in humans and animals. The most well-known mycobacterial species is Mycobacterium tuberculosis, which causes tuberculosis, a serious respiratory illness. In addition to Mycobacterium tuberculosis, there are other species like Mycobacterium leprae, responsible for leprosy, and Mycobacterium avium, which can affect individuals with weakened immune systems. Mycobacteria are typically slow-growing, making infections difficult to diagnose and treat effectively.