Lab 4: GI tract cultures

This week in lab we were given a case along with stool cultures on CVA, XLD, Mac, and SBA.  My case stated that a 4 ½ year old boy was admitted to the ER with a high fever of a 3 day duration.  According to his mother, he had been ill with diarrhea for about a week.  The family doctor had suspected a GI infection by symptomatic treatment had not resulted in any improvement.  On admission he had a temperature of 40°C, which lasted 4 days.  His abdomen was soft and intermittently sensitive to pressure.  The child excreted large volumes of thin, slimy stools that had a strong smell. 

In order to determine the cause of the infection I examined the culture plates.  There was no growth on the CVA plate which meant that the bacteria was not Campylobacter.  The 1 isolate I identified on XLD grew bright yellow colonies with clear centers.  Clear, peachy colonies grew on Mac.  Based on these 2 plates, I suspected Yersinia sp.  I identified 2 isolates on SBA.  The 1^st grew small, gray, opaque-translucent colonies and the 2^nd isolate grew small, white, opaque, convex colonies.  Because the 2^nd isolate did not grow on XLD or Mac I suspected a gram positive organism.  Based on colony morphology on SBA I presumptively identified isolate 2 as coagulase negative Staphylococcus. An API 20E confirmed the 1^st isolate as Yersinia enterocolitica.



Isolate 1 - Yersinia enterocolitica




Isolate 2 - Coagulase negative Staphyloccus



Yersinia enterocolitica is a mild zoonotic disease that most often affects young people.  Symptoms include watery or bloody diarrhea and fever.  The bacteria replicate in the ileum and invade Peyer’s patches in the intestinal wall.  From here it can disseminate to the lymph nodes causing lymphadenopathy. This can lead to abdominal pain.  Yersinia is usually spread via contaminated pork or water but can be shed in stools by infected individuals.  The child could have contracted the bacteria from someone in his school or from eating contaminated foods.