TeachableMedicalNews article 07162019

Teachable moment in classrooms:

  1. cellular basis of life chapter – ligand-receptor interaction
  2. urinary system chapter – glomerular filtration through capillaries of glomerulus
  3. immune system chapter – normal immune functions destroy E. coli that enters the body; consequences of immunosuppressed state

 

Why E. coli outbreaks can be deadly?

The news item:  In 2018 this headline informed us that E. coli infections can have deadly outcomes after consuming the contaminated romaine lettuce:

E. coli outbreak linked to romaine turns deadly | CNN

One person has died from the E. coli outbreak linked to romaine lettuce from the Yuma, Arizona, growing region. The death, in California, is the first known fatality from this outbreak.

 

The article mentions the symptoms of diarrhea, cramps resulting from infection by some E. coli strains.  The article also mentions the deadly affliction of hemolytic uremic syndrome.

So, Why Do I Care??  At first look this looks like fake news; we carry trillions of E. coli bacteria in our large intestine, so why just a little extra could make us sick or kill us?  However, a few very special types of E coli can damage our bodies severely. Those special types of E coli seeks out the most vulnerable among us: the elderly, the cancer patients, the people with organ transplants, basically anyone with a depressed immune system.  The overall mortality rate is between 5 and 15%, but among the immunosuppressed the mortality may rise to 25%. In addition, over half of the survivors may develop kidney failure in later years.

 

Plain English, Please!!!  First, let’s talk about E. coli. So, Escherichia coli is the Latin name of a common bacterium that lives inside of the large intestines of many animals, and in humans as well.  Most of these bacteria are harmless, but a few types of them make toxins that can hurt us badly. The harmful types of E. coli live in the large intestine of cattle, sheep, pigs, deer, rabbits, birds, and in some healthy people.  So, contamination of food items with animal or human fecal matter is how the harmful E. coli get into our bodies.

Second, let’s talk about how the harmful E. coli can cause life-threatening disease.   Those kinds of E. coli make chemicals called toxins, in this case the Shiga toxin.  Those toxins attack the smallest blood vessels first in the intestines, and then in the kidneys.  The damage to those blood vessels in the intestines causes bloody diarrhea, and the damage in the kidneys causes kidney failure.  Our kidneys filter blood through small blood vessels, so damage to those blood vessels stop kidney function, and thus causes kidney failure.  The toxins also damage red blood cells by making them burst open.  The official name to such disorder is hemolytic uremic syndrome.

So, then how come that some people and many animals carry those harmful E. coli without any sign of disease?  The toxins are harmful only if they bind to a receptor molecule on the cells.  Picture your fingers sliding into a glove.  That’s how a toxin has to fit into a receptor on the cells.  If the glove is not there (like in most animals, or if the glove is missing fingers (like in some resistant people) the toxin can not interact with a cell, and so, the toxin can not cause harm.

What about people who get infected by harmful E. coli, but has only a mild disease?  In those individuals the normally functioning immune system destroys the E. coli that enter the tissues and the blood stream.