lab 4-7: Hektoen Enteric agar

purpose?

to presumptively identify the shigella and salmonella genera using hektoen enteric agar.

what carbohydrates are included in this media? why?

lactose, sucrose, salicin. these are included because the non-coliforms do not ferment them (our focus)

what is the specific reason why sodium thiosulfate is included in the media?

Sodium thiosulfate is included to test for the formation of hydrogen sulfide gas. This distinguished the salmonella organisms which are able to metabolize thiosulfate

what ingredients make the agar selective and differential?

bile makes this selective as it filters out gram +.

differential ingredients include:

• lactose, sucrose, salicin as these are not fermented by non coliforms

• bromthymal blue to visually highlight the organism that ferment the sugars

• thiosulfate for the creation of hydrogen sulfide gas (only done by salmonella)

• iron to visually highlight the created H2S gas

list one genera that can produce blue-green growth without any black precipitate. What disease is linked with this genera? is this genera classified as coliform or non?

Shigella can produce blue-green growth without black. this genera causes shigellosis, which is a bloody diarrhea (dysentary) that is transmitted fecal oral. This genera is a non coliform as it does not ferment lactose.

why is lactose included in this experiment ?

lactose is included since it is the primary carb fermented by coliforms. + lactose fermentation = + coliform

describe what result a coliform would give in this experiment and why?

a coliform would result in positive growth with an orange color. This orange color would result from the fermentation of the present carbs, resulting in acid

describe what salmonella cholerasius would look like?

• + growth

• - acid (so dark green/blue plate)

• + black from H2S present

list two diseases linked to salmonella. How are these diseases transmitted?

• salmonellosis = food poising. treatment is replenishment of fluids

• typhoid fever = food poisoning. treatment is antibiotics

the development of black buildup means ___ gas was produced?

hydrogen sulfide