Enterohemorrhagic E. Coli (ehec)

by Vincent Racaniello, PhD

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    00:01 Alright so that's the shigella causing dysentery, that's their mechanism of causing it, let's move to E. coli, one kind of E. coli, enterohemorrhagic E. coli or EHEC. Now these are strains of E. coli that are frequently in the news, so you may have heard of them, EHEC E. coli, they cause non-febrile, no fever bloody diarrhea and hemorrhagic colitis is the name of this syndrome when caused by the EHEC strains.

    00:29 So how does this work? These are strains of E. coli that produce toxins, they produce a shiga-like toxin which we've heard about before, can cause ion imbalances leading to water secretion and there are several names for these strains as a consequence, besides EHEC, they're also called STEC, which means shiga-like toxin producing E. coli or HUSEC, hemolytic uremic syndrome-associated enterohemorrhagic E. coli, as we'll see that's one of the syndromes associated with infection or verocytoxin -producing E. coli, VTEC strains, all these are the same name for EHEC type strains. They are often classified according to the O-antigen here, we're showing lipopolysaccharide, which is a component of the outer membrane of these gram-negatives, you may remember this, if not you can go back to one of the earlier lectures in which we talked about this in detail. One of the components of LPS is the O-antigen, which you can see at the top there, and the O-antigen is how we categorize many of these strains. And so for example you probably have heard of E. coli O157:H7. This is a strain that has caused many outbreaks of dysentery and it's often acquired from cows, if you eat undercooked hamburger, you can be infected with an O157 strain. The cows have this bacterium in their intestines, it does not harm them whatsoever, but if it gets to you somehow, either via the meat, the meat can easily be contaminated with cow feces during the preparation, if you don't cook it enough you don't kill the organism, you'll get infected, you'll get the diarrheal disease from it. You can also get it from contaminated water. Again, if the water is contaminated with manure in some way by improper preparation, you will get this disease. O157 is a specific kind of O-antigen, so now you know what this means, the lipopolysaccharide, those O-antigens at the very top in the previous side, that's what it's categorizing this as O157. And if you're interested, the H7 is a flagellar antigen.

    02:44 The flagellum is the molecule that propels these bacteria around to move, this is one of the proteins of the flagellum, the H protein. So now you know that these EHEC strains are categorized by lipopolysaccharide and flagellar antigens. These bacteria may cause something called hemolytic-uremic syndrome and this is accompanied by hemolytic anemia, the red blood cells are lysing, so you become anemic, you have not enough red blood cells, thrombocytopenia and kidney failure.

    03:18 These are all associated with these EHEC infections. A very large outbreak of an EHEC strain occurred a number of years ago in Germany and these were caused by a slightly different strain, a brand-new one that hadn't been seen before, O1O4:H4. And now you know exactly what the O and the H antigens are. This caused a big outbreak in Germany, a foodborne disease and it was traced to contaminated vegetables. It was actually an EAggEC strain. Now we talked about the EAggEC strains as causing diarrhea in AIDS patients, somehow this EAggEC strain acquired a gene for the shiga toxin which causes the watery diarrhea, producing this new strain O1O4:H4. It was present on vegetables, probably via contamination with dirty water and it wasn't washed properly and if you eat uncooked vegetables and you know, people do like to eat their carrots uncooked and even cucumbers and sprouts, particularly sprouts are never cooked and so these are common ways to get this infection. But this is an interesting case where the shiga toxin had been newly acquired by one of these other strains. In the bowel, these EHEC strains produce proteins that allow them to attach and efface like the EPEC strains, not all of them produce toxins, this particular strain in the German outbreak had acquired a shiga-like toxin, but mostly EHEC strains simply attach and efface the surface of the villi and that causes the diarrhea. The production of a shiga-like toxin, if it's present may be responsible for a cytokine response in the mucosa, you can get profuse bleeding and this is caused by interaction of the cytokines that we produce with the shiga toxins which damage the blood vessel and a major complication as I mentioned is this hemolytic uremic syndrome. This is a combination of damage to small blood vessels, if this happens in the kidney, you'll have kidney problems and if you have extensive lysis of red blood cells, the remaining pieces of the red blood cells get hung up in the kidney, further complicating kidney function. These strains can also invade the brain, where it can cause thrombocytopenic purpura and the shiga toxins are on phages. And again the shiga toxin originally seen in shigella, causing the loss of water from the intestine, these are on phages so they're mobile. These toxins can spread from bacteria to bacteria and that's presumably why the E1O4 German strain arose by infection with a phage that deliver the shiga toxin gene at some point. These toxins are taken into cells and inhibit protein synthesis.

    About the Lecture

    The lecture Enterohemorrhagic E. Coli (ehec) by Vincent Racaniello, PhD is from the course Bacteria.

    Included Quiz Questions

    1. Shiga toxin
    2. Cholera toxin
    3. LT toxin
    4. ST toxin
    5. Intimin
    1. Travelers diarrhea
    2. HUS
    3. Shiga toxin
    4. Undercooked hamburger meat
    5. Contaminated water
    1. Bloody sputum
    2. Kidney failure
    3. Thrombocytopenia
    4. Lysis of red blood cells
    5. Small blood vessel damage

    Author of lecture Enterohemorrhagic E. Coli (ehec)

     Vincent Racaniello, PhD

    Vincent Racaniello, PhD

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