Microbiology Case Study: 2 Year Old with Fever and Bloody Diarrhea



A 2-year-old male with no past medical history presented to the emergency department with fever and 2 days of bloody diarrhea.  Stool cultures were sent to the laboratory.  A Gram stain of the specimen showed the morphology seen in Figure 1. On the 5% sheep blood agar plate, the predominant organism had colonies that appeared flattened and spreading (Figure 2A).  On MacConkey agar the colonies were noted to be non-lactose fermenting (Figure 2B).  A Hektoen enteric (HE) agar was used as a differential and selective media to differentiate Salmonella from Shigella.  On the HE agar the colonies were clear with a green appearance due to the color of the agar (Figure 2C).



Shigella is a bacterium in the Enterobacteriaceae family and is a Gram-negative rod that is facultatively anaerobic. It is non-motile, a non-spore former, and does not ferment lactose.  There are four species of Shigella

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