Yersinia enterocolitica

00:00 / 00:00



Yersinia enterocolitica


Introduction to bacteria

Bacterial structure and functions


Yersinia enterocolitica


0 / 10 complete

USMLE® Step 1 questions

0 / 1 complete

High Yield Notes

17 pages


Yersinia enterocolitica

of complete


USMLE® Step 1 style questions USMLE

of complete

An 11-year-old boy is brought to the emergency department due to fever and abdominal pain. Symptoms started two days ago and the abdominal pain has worsened. In addition, the patient is refusing to eat and vomited three times the day before the presentation. Physical examination shows tenderness to palpation in the right lower quadrant of the abdomen. Temperature is 38.7 ºC (101.7 ºF), pulse is 114/min, blood pressure is 103/70 and respirations are 10/min. Abdominal ultrasound shows no inflammation or enlargement of the appendix. MRI of the abdomen shows a normal-appearing appendix but several enlarged mesenteric lymph nodes. Stool studies show Gram-negative, oxidase-negative, non-lactose-fermenting bacteria. Which of the following is the most likely cause of this patient’s condition?  

External References

First Aid









Yersinia enterocolitica p. , 142

Yersinia enterocolitica p. , 142, 176


Yersinia enterocolitica is a Gram-negative bacillus that belongs to a family of bacteria called the Enterobacteriaceae.

The Yersinia genus got its name from Alexandre Yersin, who discovered it, and enterocolitica refers to intestine and colon, so Yersinia enterocolitica causes a diarrheal illness, called yersiniosis.

Now, a little bit of microbe anatomy and physiology.

First, Yersinia enterocolitica has a thin peptidoglycan layer, so it doesn’t retain the crystal violet dye during Gram staining.

Instead, like any other Gram-negative bacteria, it stains pink with safranin dye.

And since it’s a Gram-negative bacillus, it looks like a little pink rod under the microscope.

Interestingly, Yersinia enterocolitica can be both motile and non-motile depending on the temperature.

So, at 25 degrees Celsius it’s motile and at 37 degrees Celsius it’s non-motile.

It’s facultative anaerobe, so it can survive in both aerobic and anaerobic environments, and also facultative intracellular which means it can survive both outside and inside the cells.

Finally, it’s non-spore forming, so it doesn’t make spores, and oxidase negative, so it doesn’t produce this enzyme.

Yersinia enterocolitica grows well on MacConkey agar, which is a medium that contains a pH sensitive dye and lactose.

This medium helps identify whether Gram-negative bacteria are lactose fermenters or not.

Some Enterobacteriaceae, like Klebsiella, Escherichia coli and Enterobacter, can ferment lactose, which results in the production of acid, and this makes the pH sensitive dye turn pink - so their colonies will be pink.

Yersinia enterocolitica, however, is a non-lactose fermenter, so it forms colorless colonies on MacConkey agar.

Yersinia enterocolitica also grows on Cefsulodin-Irgasan-Novobiocin agar, or CIN agar for short.

After 24 hours of incubation, it forms white, sharp-bordered colonies with a deep-red center, that looks like bull’s eyes colonies.

Finally, the triple sugar iron test, or TSI for short can be done to assess hydrogen sulfide production.

This medium contains three sugars - lactose, glucose and sucrose, as well as iron and a pH sensitive dye.

If the bacteria produces hydrogen sulfide, that reacts with the iron, and a black precipitate forms in the test tube.


Yersinia enterocolitica is a Gram-negative bacterium belonging to the Enterobacteriaceae family that causes a diarrheal illness called yersiniosis. It secretes bacterial proteins called Yops, which block the secretion of proinflammatory cytokines and inhibit macrophage activation. Yersinia enterocolitica is transmitted through pet feces, contaminated milk, or pork and causes a gastrointestinal infection that can mimic appendicitis. It can spread systemically and cause septicemia, which can be rapidly fatal if left untreated. Even after the infection, there may be associated sequelae such as reactive arthritis and erythema nodosum.


Copyright © 2023 Elsevier, its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Cookies are used by this site.

USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.