Compare the recipes of nutrient agar and HE agar If an organ

Compare the recipes of nutrient agar and HE agar. If an organism can grow on both media, on which would you expect it to grow better? Explain your answer.

Solution

Recipe of nutrient agar:

Peptone - 5g

Meat extract - 3g

Agar - 15g

Water - 1000 ml (final volume)

Ph = 7

Ingredients of HE agar includes peptone, yeast extracts, protease, peptone, bile salts, sodium chloride, sodium thiosulfate and ferric ammonium citrate.

Hektoen Enteric agar (HE agar) is an undefined medium used to differentiate the species of Salmonella and Shigella species from the other enterobacter species. This is based on their ability to ferment lactose, sucrose or salicin and the reduction of sulphur (indicate by the production of hydrogen sulphide gas). The metal ion in the ferric ammonium citrate react with the H2S, which forms a black precipitate (indicates the sulphur reduction). The media also contains bile salts, which inhibit the growth of Gram-positive cocci. The colour indicators used are bromothymol blue and fuchsine dyes.

So, when we grow an organism on both media, the organism better grows on nutrient agar because they are no inhibitory compounds in it. HW agar is selective and differential.