Colonizes human gastrointestinal tract but does not cause disease

Escherichia coli strain HS. 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). It was obtained from Drs. Kaper and Nataro at the School of Medicine at the University of Maryland. 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. It is competent and amenable to genetic manipulation.