What is the economic importance of bacteria?
Bacteria can be negative. Bacteria cause many diseases, such as cholera, typhoid, and tetanus. While many of these diseases are treatable and/or preventable with antibiotics, proper sanitation, and vaccines, they are still a problem in the developing world and cost businesses billions of dollars a year because of lost productivity (many employees have to take sick days because of bacteria-caused illnesses). Bacteria also cause food spoilage. The waste products of bacterial metabolism is what causes food to go bad, and this costs grocery stores and food producers billions of dollars per year.
That said, bacteria are not entirely bad. You need a certain amount of bacteria in your stomach to digest food, and your doctor may prescribe a probiotic if you are taking antibiotics to ensure your stomach has the proper amount of bacteria. Cows and other ruminants need bacteria to digest the cellulose in plants. Bacteria in soil break down plant and animal matter in order to make nutrients available for plants—without bacteria, plants would not have enough food and the world would experience widespread famine. Bacteria also assist in making beer and cheese.