Bacteria are single-celled microorganisms that exist under all conditions of life, and are of tremendous consequences to humans serving many functions, some beneficial and some harmful. They thrive by living on dead organic matter. Beneficial bacteria are useful in the production of food products including dairy products such as yogurt, sauerkraut, fermented meat products, and vinegar. They also help fix nitrogen in the soil and are responsible for decomposing organic materials, returning important nutrients back to the soil. Pathogenic bacteria produce diseases in humans, animals and plants by growing on or in certain tissues and producing harmful poisons or toxins. They may cause illnesses such as bacterial pneumonia, strep throat, and most ear infections.