Lab Media Tests

Hektoen enteric agar

*selective and differential agar (contains indicators for lactose fermentation and hydrogen sulfide production)
*contains inhibitors to prevent gorwth of gram positive bacteria
*contains peptone (carbon source)

*used to recover salmonella and shigella from patient specimens

*lactose, sucrose, salicin

*Bacteria other than shigella and salmonella will acidy the medium (because they use the sugars instead of peptone) turning it yellowed

*peptone metabolism (carbon source) by Shigella and Salmonella alkalises the medium (turning it blue)

*thiosulfate or ferric ammonium citrate
*when there is H2S present

Shigella colonies looks green because it does not produce H2S (doesn't react with Thiosulfate or ammonium citrate to produce black precipitate)

Salmonella colonies look black (they produce hydrogen sulfide in response to the thiosulfate or ferric ammonium citrate in the HEA media)

*Salmonella, found in intestines

Detects the presence of the catalase enzyme
*positive (has catalase-presence of bubbles)
*negative (no catalase-non bubbles)

*splits H2O2 into oxygen and water

Positive catalase rx

Negative catalase rx

*gram positive
*non-spore forming cocci