prop. n. (Microbiol.) a natural family of rod-shaped gram-negative bacteria, most of which occur normally or pathogenically in intestines of humans and other animals, and some of which grow in plants. The type genus is Escherichia. They are aerobic and facultatively anaerobic, and may be motile or non-motile. Most are easily cultured on artificial growth media. Both pathogenic and non-pathogenic strains exist. [ PJC ]