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.
-You take a stool sample from Mrs. Thomas, and send it to the lab for analysis. You tell her that the technicians will do a variety of tests to confirm the identity of the organism causing her illness. The first thing that will be done is to inoculate some of her stool sample onto a medium called hektoen enteric (HE) agar. On this medium, Shigella species produce blue-green colonies, while Salmonella produces blue-green colonies with a black center, and most Gram-positive bacteria do not grow at all. You explain to Mrs. Thomas that this type of medium is called a(n) ________ medium.
A) selective
B) differential
C) enrichment
D) selective and differential
E) differential and enrichment

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.
-You take a stool sample from Mrs. Thomas, and send it to the lab for analysis. You tell her that the technicians will do a variety of tests to confirm the identity of the organism causing her illness. The first thing that will be done is to inoculate some of her stool sample onto a medium called hektoen enteric (HE) agar. On this medium, Shigella species produce blue-green colonies, while Salmonella produces blue-green colonies with a black center, and most Gram-positive bacteria do not grow at all. You explain to Mrs. Thomas that this type of medium is called a(n) ________ medium.
A) selective
B) differential
C) enrichment
D) selective and differential
E) differential and enrichment

Quizplus · Accepted Answer

Hektoen enteric (HE) agar is both selective and differential. It is selective because it contains bile salts and dyes that inhibit the growth of many Gram-positive bacteria and some Gram-negative bacteria, allowing for the isolation of Gram-negative enteric bacteria. It is differential because it contains indicators that allow for the differentiation of various enteric bacteria based on their ability to ferment lactose or sucrose and produce hydrogen sulfide gas. The distinction between Shigella and Salmonella is based on the production of hydrogen sulfide gas, which causes the center of the colony of Salmonella to turn black.

Mrs Thomas Comes to the Emergency Department Where You Work