Putrefaction, the decomposition of nitrogenous and other organic materials in the absence of air, produces foul odors. Decay is the gradual decomposition of organic matter exposed to air by bacteria and fungi. Once attached, the bacteria may produce poisonous substances called toxins. Endotoxins stimulate production of cytokines that can produce widespread vasodilation and shock. Many chemical substances are produced as a result of bacterial activity, among them acids, gases, alcohol, aldehydes, ammonia, carbohydrates, and indole.
Pathogenic forms produce hemolysins, leukocidins, coagulases, and fibrolysins.
Groups of cells can then be examined under a microscope, usually with Gram's stain. In addition, colonies can be separated and antibiotics applied to assess their sensitivity to different drugs. Bacteria are often described by a combination of their response to Gram's stain and their appearance. Bacteria stained with fluorescein and examined under a microscope equipped with fluorescent light appear yellow-green. Taber's Cyclopedic Medical Dictionary, Edition 18.