Use a marker to divide a Hektoen enteric agar plate into thirds. Label the plate

Question

Use a marker to divide a Hektoen enteric agar plate into thirds. Label the plate with your name and lab time, and label each section of the plate with the name of the appropriate organism. Using a loop, make a single small streak of each culture onto the appropriate section of the plate. Incubate the plate at 37 degree C for 24-48 h. A mixed culture containing E. coli, Salmonella choleraesuis, and Enterococcus faecalis is streaked onto Hektoen enteric agar. E. coli is a Gram-negative lactose fermenter that produces hydrogen sulfide, S. choleraesuis is a Gram-negative nonfermenter that produces hydrogen sulfide, and E. faecalis is a Gram-positive, lactose fermenter. Explain the appearance of each species after incubation of the plate.

Explanation / Answer

Hektoen enteric agar contains bile salts and dyes. It is used as a differential and selective medium. It inhibits the growth of gram positive organisms. E.coli produces yellowish-orange colonies, S.choleraesuis produces greenish colonies and E.faecalis produces yellowish-pink colored colonies.

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