Bacteria are single-celled microorganisms that are found in every environment on Earth. They come in various shapes and sizes, with some being spherical, rod-shaped, or spiral. Despite their small size, bacteria play a crucial role in the ecosystem by decomposing organic matter and recycling nutrients. They also live in and on the bodies of plants and animals, both as beneficial symbionts and harmful pathogens. Some bacteria are harmful to human health and can cause infections and diseases, while others are used in various industries, such as food production and medicine. Antibiotics are commonly used to treat bacterial infections, but overuse and misuse have led to the emergence of antibiotic-resistant bacteria, posing a growing threat to public health.