Gangrene
Gangrene
Gangrene is a disease that is caused most frequently by the bacterium Clostridium perfringens, which can live in the absence of oxygen. In an infected wound, growth of the bacterium and resulting production of a toxin results in the death of human tissue. Tissue death is usually due to ischemia, which is an interruption in the blood supply to a particular area. Loss of blood supply means loss of oxygen delivery to that tissue, as well as loss of other nutritive factors usually carried in the blood circulation. Tissue deprived in this manner will die, and often becomes even further infected with bacteria during this process.
Gangrene was a disease associated with wartime, particularly with ill-attended wounds that became exposed to dirt (a habitat of C. perfringens ). Nowadays, in the developed world gangrene is more typically associated with the presence of atherosclerotic disease (disease in which arteries are stiff and hard, with fatty deposits blocking blood flow). The interrupted blood flow to toes, feet, and legs, as well as the lack of pain sensation that can accompany the impeded circulation, is a major predisposing factor to gangrene, particularly of the toes, feet, and legs.
In addition, people with diabetes often have advanced, severe cases of atherosclerosis, as well as a condition called neuropathy. Neuropathy is a type of nerve disease, which results in a significant decrease in sensation. Diabetics may not be able to feel any pain from a relatively minor injury (for example, a developing blister) to their foot or leg. Because the diabetic patient does not feel the blister, due to neuropathy, and because the blood supply to the area is so severely compromised, a small initial area of damage can be
extremely difficult to heal, and can rapidly spread. Furthermore, any small opening in the skin, such as a blister, can provide an entry point for bacteria (most commonly staphylococcal and/or streptococcal bacteria) The combination of tissue damage from a blister, along with lack of blood supply to the area to either help in healing the blister or in delivering immune cells to fight infection, can result in the ultimate development of gangrene from a seemingly insignificant injury. This can be severe enough to require amputation of part or all of the affected body part.
Gas gangrene
The scenario most frequently called to mind by the word gangrene is of an extremely rapidly progressing disorder, classically affecting a leg wounded in battle, and resulting in a blackening of the limb which leads either to death of the individual or amputation of the limb to save that person’s life. In fact, this scenario is due to a very specific form of gangrene called “gas gangrene.” Individuals who suffer bullet wounds during the course of battle are very likely to have had these wounds contaminated with dirt or with shreds of their own clothing. This can introduce C. perfringens or related clostridia into the wound. Some types of extreme injury in civilian life can also result in C. perfringens infection. Because C. perfringens bacteria sometimes reside within the gallbladder, spillage of gallbladder contents during surgery can result in gas gangrene of the abdominal muscles.
C. perfringens causes much of its effect due to its ability to produce toxins, or poisons. In fact, C. perfringens is a close cousin to the bacteria which cause tetanus (C. tetani ) and food poisoning, called botulism
KEY TERMS
Atherosclerosis —Abnormal narrowing of the arteries of the body that generally originates from the buildup of fatty plaque on the artery wall.
Ischemia —Decreased blood, and therefore oxygen, supply to a particular area.
Neuropathy —Decreased functioning of the peripheral nervous system. In diabetes, neuropathy leads to decreased sensory perception, and starts in the feet and lower legs.
(C. botulinum ). These bacteria also produce their effects through the production of toxins.
Gas gangrene receives its name from another characteristic of the C. perfringens bacteria. These bacteria ferment (breakdown) certain chemical components of muscle, giving off gas in the process. During examination of the affected area, one can actually feel bubbles of gas which have risen up just under the layers of skin.
C. perfringens bacteria multiply so quickly that gas gangrene can develop in a few hours. An individual with gas gangrene will note severe pain at the wound site (if the pain sensation has not been dulled), with increasing swelling of the area. The wound will begin to give off a watery, sometimes frothy fluid, which has a unique sweet odor, probably due to the digestion of muscle carbohydrate by the bacteria. As muscle breakdown progresses, the muscle feels cooler and appears paler than normal. The muscle feels softer and more liquid, as the bacterial toxins actually work to liquefy it. Ultimately, the area turns a deep blue-black, the classic color of gangrenous tissue. Low blood pressure, kidney failure, and a state of shock (severely decreased blood circulation to all major organ systems) may set in. Survival time for an individual with untreated gas gangrene can be as short as a single day.
Treatment of gas gangrene is with massive doses of antibiotics, in particular Penicillin G. Surgical removal of infected tissue, with a wide margin around it, is necessary to hal the spread of infection, and gangrenous limbs may require amputation.
A fascinating type of treatment for gas gangrene is hyperbaric oxygen therapy. The therapy involves placing an individual in a completely closed, carefully pressurized space, within which the patient will breathe 100% oxygen (much higher than the 21% oxygen
present in normal room air). This high level of oxygen reaches the tissues, where it slows the multiplication of the bacteria, inactivates toxin, and decreases further toxin production.
Resources
BOOKS
Freeman, Frank R. Gangrene and Glory: Medical Care during the American Civil War. Chicago: University of Illinois Press, 2001.
Icon Health Publications. Gangrene: A Medical Dictionary, Bibliography, and Annotated Research Guide to Internet References. San Diego: Icon Health Publications, 2004.
Kobayashi, G., Patrick R. Murray, Ken Rosenthal, and Michael Pfaller. Medical Microbiology. St. Louis, MO: Mosby, 2003.
Rosalyn Carson-DeWitt