A genus of bacteria named for Theodor Escherich, an Austrian pediatrician and bacteriologist, who first published on these bacteria in 1885. Escherichia coli is the most important of the six species which presently make up this genus, and it is among the most extensively scientifically characterized living organisms. Escherichia coli are gram-negative rod-shaped bacteria approximately 0.5 × 1–3 micrometers in size.