From the CDC: “This photograph depicts the colonial growth pattern displayed by Salmonella typhimurium bacteria cultured on a Hektoen enteric (HE) agar medium; S. typhimurium colonies grown on HE agar are blue-green in color, for this organism is a lactose non-fermenter, but it does produce hydrogen sulfide, (H2S), therefore there can be black-colored deposits present.
HE agar is the medium designed for the isolation and recovery of fecal bacteria belonging to the family, Enterbacteriaceae. S. typhimurium causes 25% of the 1.4 million Salmonellosis infections a year in the United States. Most persons infected with Salmonella sp. develop diarrhea, fever, and abdominal cramps 12 – 72 hours after infection. The illness usually lasts 4 – 7 days, and most people recover without treatment. However, in some cases, the diarrhea may be so severe that the patient needs to be hospitalized.”
Image Credit: CDC