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wk 6A prelab

wk 6A prelab - organisms that aren’t esculin-positive in...

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1. Because mannitol is the substrate for fermentation, it is differential because the fermentation products will be indicated by a color change in phenol red. It is differential because it separates most staphylococci that don’t use mannitol from the S. aureus species that does. 2. Organisms at the bottom of the plate are staphylococci besides S. aureus because they grew well but did not ferment mannitol. The organism on the top is S. aureus because it grew well and fermented mannitol, turning the indicator yellow. 3. Many organisms can only hydrolyze esculin under acidic conditions or tolerate bile but not both at the same time. But of streptococci, only enterococci and members of the S. bovis group can hyrdolize esculin in the presence of bile and tolerate bile. This differentiates esculin-positive bacteria from other streptococci and selects against
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Unformatted text preview: organisms that aren’t esculin-positive in the presence of bile. 4. Esculin was hydrolyzed to beta-D glucose and Esculetin, forming a dark brown iron precipitate that is deposited in the media. 5. The classical method took 48 hours and tested for the presence of benzoic acid in hippurate hydrolysis. The rapid method is two and a half hours, uses the enzyme hippuricase and tests for the presence of glycine. 6. MacConkey allows for differentiation among members of the Enerobacteriaceae family because lactose fermenters turn pink while others stay colorless. 7. All three innoculations require more time to grow for results to be seen, so the results can be recorded on day 2. They also differentiate and select among large groups of bacterial families and this helps preliminarily to narrow down the what the unknowns could be....
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