General Information: This strain (HS; serotype O9) is a human commensal that was originally isolated from a laboratory scientist at Walter Reed Army Institute of Research in 1978 (Levine, 1978). Strain HS colonizes the human gastrointestinal tract in challenge experiments, but no overt signs of disease occur. Thus, this strain represents a genomic baseline for human gastrointestinal tract colonization. This organism was named for its discoverer, Theodore Escherich, and is one of the premier model organisms used in the study of bacterial genetics, physiology, and biochemistry. This enteric organism is typically present in the lower intestine of humans, where it is the dominant facultative anaerobe present, but it is only one minor constituent of the complete intestinal microflora. E. coli, is capable of causing various diseases in its host, especially when they acquire virulence traits. E. coli can cause urinary tract infections, neonatal meningitis, and many different intestinal diseases, usually by attaching to the host cell and introducing toxins that disrupt normal cellular processes.