How Bacteria Cause Disease

Bacteria usually gain entrance to the body either by inhalation, by ingestion, or through a break in the skin. Once they have entered a tissue, the bacteria may produce a substance known as the spreading factor. The spreading factor digests connective tissue barriers in the tissues, thus allowing further spread of the bacteria or their toxins. Failure to overcome these invasive agents can lead to severe tissue damage. Large numbers of bacteria may compete with the healthy cells for nutrients and oxygen. Toxins, on the other hand, disrupt normal cell metabolism by interfering with chemical reactions. When a tissue becomes infected by bacteria, white blood cells migrate to the site of infection and begin to ingest the bacteria. The bacteria, however, may survive and multiply within the white cells, which then burst, releasing the bacteria into the tissue once again, causing severe inflammation. More white cells then enter the area to try to combat the infection. White blood cells are attracted to an infected site where bacteria are multiplying and causing inflammation. Some bacteria have thick capsules around them which prevents them from being engulfed, consequently, the bacteria increase. The body then manufactures antibodies which attach themselves to the bacteria, making them vulnerable to ingestion by the white cells. In this illustration the infected site is supplied with white blood cells. The bacteria have gained entry by a small cut in the skin and are beginning to multiply and grow rapidly, secreting toxins which can act locally or can enter the general circulation to be widely dispersed, causing the death or malfunction of the body cells. If the white cells fail to combat the bacteria in the initial stages, then tissue damage may occur. If they initially fail to destroy the bacteria, then the bacteria increase in number and finally begin to break up, releasing toxic chemicals, called endotoxins, which are contained with their walls. The released endotoxins may cause local tissue damage.