Bacteria are microscopic single-celled organisms found virtually everywhere on Earth—in soil, water, and living organisms including humans. While some bacteria cause illness (like strep throat or food poisoning), many are beneficial or essential for life. Gut bacteria help digest food, soil bacteria cycle nutrients, and bacteria are used in producing foods like yogurt and cheese. In public health contexts, bacterial infections are treated with antibiotics, though antibiotic resistance is a growing concern. Water treatment, food safety regulations, and sanitation practices all aim to control harmful bacteria while recognizing that most bacteria are harmless or helpful.