Bacterial parasites that cause disease are called pathogens. Among bacterial plant diseases are leaf
spot, fire blight, and wilts; animal diseases caused by bacteria include tuberculosis, cholera, syphilis,
typhoid fever and tetanus. Some bacteria attack the tissues directly; others produce poisonous substances
called toxins. Natural defense against harmful bacteria are provided by antibodies in the blood. Certain
bacterial diseases, e.g., tetanus, can be prevented by injection of or of serum containing antibodies
against specific bacterial antigens; immunity to some can be induced by; and certain specific bacterial
parasites are killed by antibiotics.
New strains of more virulent bacterial pathogens, many of them resistant to antibiotics, have emerged in
recent years. Many believe this to be due to the overuse of antibiotics, both in prescriptions for minor,
self-limiting ailments and as growth enhancers in livestock; such overuse increases the likelihood of bacterial
mutations. For example, a variant of the normally harmless Escherichia coli has caused serious illness and
death in victims of food poisoning.
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