Enterohemorrhagic Escherichia coli (EHEC) – A Index(first) Case at Tribhuvan University and Teaching Hospital (TUTH)


I with my colleague were working in our microbiology laboratory, TUTH, Nepal on a case of taeniasis when a patient came to us. He was referred from surgery OPD for stool routine examination to rule out infective cause. The stool sample he provided was completely blood. We examined his stool and found nothing else but only erythrocytes (RBC). So, we thought it was bleeding per rectum (hematochezia-a surgical problem) rather than a bloody stool due to some infective causes. But still, we requested him to bring his next day stool sample due to his history of consumption of food on local restaurant a day before the onset of symptoms.

On next day his stool was bloody macroscopically (fig. 1,2) and on microscopy examination, we found cysts and trophozoites of Giardia lamblia with plenty of erythrocytes in his stool but no pus cells. As Giardia does not cause bloody diarrhea, we thought the cause could be something else, probably Enterohaemorrhagic Escherichia coli or others. So, we cultured his stool sample simultaneously in MacConkey agar and Sorbitol MacConkey agar and incubated it at 37 degree celcius overnight aerobically. Next day when we observed the culture plates, we found that MacConkey agar had only lactose fermenting (pink) colonies whereas Sorbitol MacConkey agar had both sorbitol fermenting (pink) and sorbitol Non-fermenting (pale) colonies. Biochemical test of the pale colonies from Sorbitol MacConkey agar was done and they were also subcultured in MacConkey agar and incubated at 37 degree celcius overnight aerobically. The next day, MacConkey agar showed lactose fermenting (pink) colonies and biochemical tests revealed that the organism was Esherichia coli. We consulted with our professors with all the evidence, they advised us to do serotyping and on serotyping Esherichia coli O157 was identified.



Fig. 1 ( patient stool sample notice the reddish color)




Fig. 2



Sorbitol fermenting (pink) colonies and Sorbitol Non-fermenting (pale) colonies on Sorbitol MacConkey agar



Sorbitol fermenting (pink) colonies and Sorbitol Non-fermenting (pale) colonies on Sorbitol MacConkey agar



Biochemical test of Sorbitol Non-fermenting (pale) colonies from Sorbitol MacConkey agar revealed Escherichia coli




Giemsa stain of the stool sample showing kite shaped trophozoites of Giardia lamblia



Thanks to Dr. Shusila, Dr. Neha and Dr. Mahesh for helping me in each and every steps to make this diagnosis possible and A big thanks to Professor Dr. Bharat Mani Pokharel, Hari Prasad Kattel, Dr. Sangita and Professor Dr. Basista Rijal for guiding us.

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