Emerging infectious diseases: Infections that are rapidly increasing in incidence or geographic range.

Endosymbiont: An organism that lives inside another organism, most often for the benefit of the two (example: rhizobia [nitrogen-fixing soil bacteria] that live within root nodules—rhizobia cannot independently fix nitrogen but need the plant as an energy source; in turn, rhizobia supply the plant host with ammonia and amino acids).

Enterohemorrhagic Escherichia coli (EHEC): A strain of E. coli that causes hemorrhage in the intestines. The organism produces Shiga toxin, which damages bowel tissue, causing intestinal ischemia and colonic necrosis. Symptoms are stomach cramping and bloody diarrhea. An infectious dose may be as low as 10 organisms. Spread by contaminated beef, unpasteurized milk and juice, sprouts, lettuce, and salami, as well as contaminated water, the infection can be serious although there may be no fever. Treatment consists of antibiotics and maintenance of fluid and electrolyte balance. In advanced cases, surgical removal of portions of the bowel may be required.

Enteropathogens: A microorganism that causes disease of the intestine.

Escherichia coli: A straight rod-shaped Gram-negative bacterium that is used in public health as an indicator of fecal pollution (as of water or food) and in medicine and genetics as a research organism and that occurs in various strains that may live as harmless inhabitants of the human lower intestine or may produce a toxin causing intestinal illness.

Eukaryotic: One of the three domains of life. The two other domains, Bacteria and Archaea, are prokaryotes and lack several features characteristic of eukaryotes (e.g., cells containing a nucleus surrounded by a membrane and whose DNA is bound together by proteins (histones) into chromosomes). Animals, plants, and fungi are all eukaryotic organisms.

Genomics: The study of genes and their associated functions.

Germ theory: The germ theory of disease proposes that specific microorganisms are the cause of particular diseases.

Gram-negative bacteria: Refers to the inability of a microorganism to accept a certain stain. This inability is related to the cell wall composition of the microorganism and has been useful in classifying bacteria.

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