Mrs. Thomas comes to the emergency department where you work, complaining of nausea and vomiting, bloody diarrhea, abdominal discomfort and fever. She tells you that she went out to a picnic the previous day, where barbecued chicken was served. Mrs. Thomas is a vegan, so she ate only salad. You think that she likely has salmonellosis, caused by the bacterium Salmonella enterica. However, the presence of blood in her stool causes you concern, and you want to rule out the possibility that patient has shigellosis, caused by Shigella bacterial species.
-On HE medium, Shigella species produce blue-green colonies, while Salmonella produces blue-green colonies with a black center. There are two noticeable types of colonies growing on the hektoen enteric (HE) medium in Mrs. Thomas' test. One type of colony is greenish in color. This leads you to conclude that the bacteria in these colonies
A) is Gram-negative and is likely Shigella.
B) is Gram-negative and is likely Salmonella.
C) is Gram-positive and is likely Shigella.
D) is Gram-positive and is likely Salmonella.
E) is Gram-neutral and is likely Salmonella.

Question

Mrs. Thomas comes to the emergency department where you work, complaining of nausea and vomiting, bloody diarrhea, abdominal discomfort and fever. She tells you that she went out to a picnic the previous day, where barbecued chicken was served. Mrs. Thomas is a vegan, so she ate only salad. You think that she likely has salmonellosis, caused by the bacterium Salmonella enterica. However, the presence of blood in her stool causes you concern, and you want to rule out the possibility that patient has shigellosis, caused by Shigella bacterial species.
-On HE medium, Shigella species produce blue-green colonies, while Salmonella produces blue-green colonies with a black center. There are two noticeable types of colonies growing on the hektoen enteric (HE) medium in Mrs. Thomas' test. One type of colony is greenish in color. This leads you to conclude that the bacteria in these colonies 
A) is Gram-negative and is likely Shigella.
B) is Gram-negative and is likely Salmonella.
C)  is Gram-positive and is likely Shigella.
D) is Gram-positive and is likely Salmonella.
E) is Gram-neutral and is likely Salmonella.

Quizplus · Accepted Answer

The greenish color of the colonies indicates that the bacteria is producing acid, and HE medium contains lactose, sucrose, and salicin as fermentable carbohydrates which are utilized by their respective bacteria to produce acid, leading to the pH indicator turning green. Shigella species produce blue-green colonies on HE medium, while Salmonella produces blue-green colonies with a black center. Therefore, the greenish colonies suggest that the bacteria is Gram-negative and likely Shigella.

Mrs Thomas Comes to the Emergency Department Where You Work