These are colonies of Escherichia coli bacteria grown on a Hektoen enteric (HE) agar plate medium; colonies of E. coli grown on HE agar display a raised morphology, and are yellow to orange-yellow in coloration.

HE agar is the medium designed for the isolation, and recovery of fecal bacteria belonging to the family Enterbacteriaceae. Escherichia coli is the most common aerobic bacteria found in the large intestine of healthy individuals, and accounts for 90 to 95 percent of all the aerobic bacteria. When E. coli is present in the diarrheal stools of infected persons, they can be passed from one person to another if hygiene, or hand-washing habits are inadequate.