What is hektoen enteric agar selective for?
BD Hektoen Enteric Agar is a moderately selective and differential medium for the isolation and cultivation of gram-negative enteric micro-organisms, especially for the isolation of Shigella and Salmonella species from fecal specimens.
Does Salmonella grow on hektoen Agar?
Hektoen enteric (HE) agar is a medium for the isolation of Shigella and Salmonella. On HE agar, Salmonella spp. produces transparent green or blue-green colonies with or without black centers and appears as almost completely black colonies. Shigella spp.
What ingredient makes hektoen Agar differential?
Lactose, sucrose, and salicin provide fermentable carbohydrates to encourage the growth and differentiation of enterics. Sodium thiosulfate provides a source of sulfur. Ferric ammonium citrate provides a source of iron to allow production of hydrogen sulfide from sodium thiosulfate, which provides a source of sulfur.
Why is hektoen enteric agar differential?
Hektoen enteric agar is a selective as well as differential media for the isolation and differentiation of enteric pathogens from clinical specimens. Since the enteric pathogens, Salmonella and Shigella can tolerate these inhibitory substances they generally grow faster and larger than the coliforms.
How does an HEK plate differentiate between E. coli Shigella and Salmonella?
Rapid lactose fermenters (such as E. coli) are moderately inhibited and produce bright-orange to salmon pink colonies. Salmonella colonies are blue-green typically with black centers from hydrogen sulfide gas. Shigella appear greener than Salmonella, with the color fading to the periphery of the colony.
Is XLD selective or differential?
XLD Agar is both a selective and differential medium. It contains yeast extract as a source of nutrients and vitamins. It utilizes sodium deoxycholate as the selective agent and, therefore, is inhibitory to gram-positive micro-organisms.
What does E. coli look like on hektoen enteric agar?
Result Interpretation on Hektoen Enteric Agar Rapid lactose fermenters (such as E. coli) are moderately inhibited and produce bright-orange to salmon pink colonies. Shigella appear greener than Salmonella, with the color fading to the periphery of the colony.
What is an example of selective media?
Selective medium contain particular ingredients that inhibit the growth of certain microbes. An example of a selective medium is MacConkey agar. It contains bile salts and crystal violet, which interfere with the growth of many gram-positive bacteria and favor the growth of gram-negative bacteria.