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E. coli - the good, the bad and the deadly

By John "Jack" Brown
University of Kansas

The presence of E. coli and other kinds of bacteria within our intestines is necessary for us to develop and operate properly, and for us to remain healthy.

Sounds weird, but, it’s true. There are billions of these little critters chugging away, making things we need, helping to digest our food, etc. They are very important to us and most of them are exceedingly kind to us indeed. Animals that are born and raised “germ free” are really wimpy. They have thin intestinal walls, puny heart output and require a lot of vitamin supplements just to stay alive.

So, when are E. coli bacteria bad for us?

Truly, you have billions of “friends” that you never knew you had. So, “What’s the big deal about E. coli?” you ask. Well, bacteria are somewhat like humans in that some humans are not very nice – and can be downright dangerous.

Of course, all humans belong to the genus/species Homo sapiens, and all E. coli belong to, well, Escherichia coli. So, just as there are individual humans, so too can different individuals exist among E. coli bacteria. We call such individuals a different “strain” of bacteria within a given species. Some of these different strains can be harmful to us.

Each of us – given the assumption that humans are reading this information – is sort of a strain of the human species, sapiens. We are different because we are genetically different. Meaning, unless we are one member of an identical twin pair, the combination of genes each of us possess is different from every other human on the face of the Earth – or arm of the Earth, for that matter.

There are about 6.5 billion humans alive on the Earth and there are probably that many bacteria in every person’s intestine. Don’t worry, they don’t take up much room, and it is possible for us to acquire an individual strain of E. coli that can mix safely with the other E. coli in our intestines.

However, this means that a particular strain of E. coli can be genetically different than the vast majority of E. coli in our intestines. If a certain E. coli strain happens to have genetic information for producing something harmful to us, then we may be in trouble.

OK, who is the bad guy?

The rare strain of E. coli that got a lot of press this fall because it is indeed a bad bug, is E. coli O157:H7, a member of the EHEC – enterohemorrhagic E. coli group. Enterohemorrhagic means an intestinally related organism, which causes hemorrhaging, and therefore, loss of blood.

Editor’s note: This expert information on E. coli is from “Bugs in the News” by John C. “Jack” Brown, Ph.D., a professor in the Department of Molecular Biosciences at the University of Kansas in Lawrence, KS. Thanks to Professor Brown for permission to use it.


How do I know? What do I do?

  • Symptoms: bloody diarrhea and abdominal cramps generally begin two to eight days after exposure. Sometimes it causes non-bloody diarrhea or no symptoms. Usually little or no fever.
  • Diagnosis: determined with a lab culture. About one-third of labs do not automatically test for it, so make sure your doctor specifically asks for the test. Anyone who suddenly has bloody diarrhea should be tested.
  • Contracted by: eating undercooked, contaminated ground beef; eating contaminated fresh vegetables; drinking raw milk; swimming in or drinking sewage-contaminated water; person-to-person contact or direct contact with contaminated surfaces, which can include produce trailers, kitchen counters and the ground, railings, feed bins and fur of livestock.
  • Prevention: cook ground beef to at least 160 degrees; avoid unpasteurized milk; wash hands before preparing or eating food; wash hands after changing diapers. Fruits and vegetables should be washed well, but washing may not remove all contamination.
  • Treatment: most people recover without any treatment within 5 to 10 days. Antibiotics should not be used. It is thought that treatment with some antibiotics could lead to kidney complications.

Source: U.S. Centers for Disease Control and Prevention