Can you identify “A” & “B” Organisms , On Hektoen Enteric (HE) Agar ?

Question mentioned , this culture media as Hektoen Entoric agar .

Remember , this media usually used to isolate and differentiate  Salmonella and Shigella species from other Gram-negative enteric  organisms.  But because of various color production , we can get clear idea about number of organisms.

This media contain , 3 sugar sources & sodium thiosulfate  is as a source of sulfur. Ferric ammonium Citrate is added to react with H2S and form a black precipitate.

Bile salts are included to inhibit most Gram-positive cocci.Proteus and  Salmonella species that  reduce sulfur to H2S  ,  And form colonies containing a black  precipitate. Therefore Organism “B” should be , Proteus or salmonella.

Also lactose fermenters , produce acid & it will produce yellow to salmon-pink color characteristic colonies on Hektoen Entoric agar . Therefore Organism “A”  must be , Ecoli bacteria. Because it has ability to ferment lactose as a enteric bacteria.

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One response

  1. Hydrogen sulfide producing organism (Black colonies) non H2S producing colonies ( yellow). Black colonies – Salmonella and Yellow colonies Shigella.

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