In laboratory examination of food samples, the results were: Gram negative staining of rods, culture on Mac Conkey media obtained pink colonies, biochemical tests of lactose fermentation (-) glucose (+), Citrate (+), SIM motility (+) sulfur (+) , TSIA H2S (+). The most appropriate conclusion from the identification results is .....

GASTROINTESTINAL PHYSIOLOGY

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Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]

In laboratory examination of food samples, the results were: Gram negative staining of rods, culture on Mac Conkey media obtained pink colonies, biochemical tests of lactose fermentation (-) glucose (+), Citrate (+), SIM motility (+) sulfur (+) , TSIA H2S (+). The most appropriate conclusion from the identification results is ____

A	Salmonella typhi
B	Escherichia coli
C	Shigella dysentery
D	Staphylococcus aureus

Explanation:

Detailed explanation-1: -This medium is both selective and differential. The selective ingredients are the bile salts and the dye, crystal violet which inhibit the growth of Gram-positive bacteria. The differential ingredient is lactose.

Detailed explanation-2: -what do you expect to see on MacConkey agar medium? lactose fermenting bacteria produce colonies that are various shades of red because of the conversion of the nuetral red indicator dye (red below pH 6.8) from the production of mixed acids. non-lactose fermenting bacteria colonies will appear colorless or transparent.

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