Bacteria do not produce antibiotics; antibiotics come from a compound that is found in fungi or another microorganism. According to the United States Centers for Disease Control and Prevention, some antibiotics are synthetically produced and do not come from microorganisms. Antibiotics are used to kill bacteria, namely those that are harmful and cause illness.
Some bacteria are "good," meaning that they are not harmful. Bacteria can develop resistance to antibiotics by mutating so that the antibiotic can no longer target them. Antibiotic resistance on the part of bacteria is a major world health concern, in part because resistant bacteria can spread easily from person to person.