Bacteria are tiny, single-celled organisms that can be found in various environments, including soil, water, and even inside the human body. They are prokaryotes, meaning they lack a nucleus and other membrane-bound organelles. Bacteria play essential roles in processes like decomposition, nutrient cycling, and even digestion in some animals, including humans. Some bacteria are beneficial, while others can cause diseases. For example, Escherichia coli is a type of bacteria that can be harmless or harmful, depending on the strain. Antibiotics are often used to treat bacterial infections, but overuse can lead to antibiotic resistance, making infections harder to treat.