CASE HISTORY A Fecal Sample from a Patient with Diarrhea Was Streaked

question 9

Essay

CASE HISTORY
A fecal sample from a patient with diarrhea was streaked onto MacConkey lactose agar medium,a medium that selectively prevents the growth of Gram-positive bacteria but will differentiate Gram-negative bacteria that can ferment lactose from those that cannot.The next day,several different types of bacterial colonies were visible on the agar plate.Some were red;others were white.The white colonies led the clinical microbiologist to suspect that the patient was infected with the Gram-negative bacillus Salmonella enterica serovar typhimurium.
MacConkey lactose agar medium selectively prevents the growth of Gram-positive bacteria but will differentiate Gram-negative bacteria that can ferment lactose from those that cannot.The use of these types of media,called selective and differential media,are extremely helpful when microbiologists already have an idea of the pathogen present.What led the microbiologist to believe that the white colonies were Salmonella enterica serovar typhimurium?

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Definitions:

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