A New and Fatal E.Coli Outbreak

05 June 2011
Posted by Chris Smith.

Dave -   Making very big headlines at the moment is an outbreak of a new strain of E. coli in northern Germany; it's thought to have stemmed from contaminated salad vegetables, including cucumbers.  The infection is a more pathogenic form of the bacteria, causing haemolytic-uraemic syndrome (HUS), which damages the kidneys and nervous system and can be fatal.  So far, about 2000 people in Europe have been infected, with at least 17 deaths.  Chris- this is your field - could you tell us a bit more about what's happening?

Chris -   Well first of all, we've probably never seen this form of E. coli before so it's almost certainly new.  It's designated E. coli 0104 and this is just a system of numbers and letters that's used to refer to the biochemical markers which are on the surface of the bug, which is a convenient way of labelling it for want of a better term.  It first cropped up in Germany late last month when it was linked to an outbreak of a form of gastroenteritis that was particularly characterised by people losing blood with the motions.  So that first of all rang alarm bells and then when the numbers really began to climb, public health officials got involved and began to trace where this may have stemmed from and also, what the causative organism was and it turned out to be this form of E. coli.  There's E. coli in the guts of pretty much everything on Earth, but some forms of E. coli tool themselves up genetically and they have this arsenal of molecular weapons that they can throw at us, and this particular strain appears to have some additional genes that enable it to produce a toxin that damages the kidneys, and can lead to blood cells breaking down and that's the haemolytic-uraemic syndrome bit of it.  So, it's an unusual form of E. coli where it came from though it's still not entirely known.

E. coli bacteriaDominic -   You said this was an entirely new strain of E.coli.  How could a new strain come about?

Chris -   Well, the really clear answer to that comes from the secrets which lurk in its genome because you can unpick, in a sort of detective way, the origins of things by asking genetically who are your relatives?  And so, what scientists have done is to send samples of this particular organism over to the Beijing Genomics Institute (BGI) which is one of the biggest genomics sequencing facilities in the world.  They have picked their way through all 5.2 million genetic letters that make up this bug, and they've began to look at what the genetic sequence is and who - in terms of microbiologically who, this organism is related to.  The interesting story that's emerged is about 93% of the genes are direct relatives from a form of E. coli which has been linked to causing diarrheal outbreaks in certain parts of Africa.  But 7% of the genome has been linked to a form of E. coli which makes toxins and in particular, toxins called shiga toxins and these toxins are nasty.  When the bug initially locks onto the wall of the intestine, it damages the wall of the intestine and then produces this toxin which oozes into the bloodstream.  And the toxin has two parts to it - a subunit A and a subunit B - and the subunit A behaves a bit like a molecular grappling hook.  It goes around in the bloodstream until it finds this structure which is on the kidney which it can bind to and it locks on, and this then helps the subunit B to crawl inside the cells where it disables the cell's ability to make proteins which are effectively the recipes that cells need to keep them alive.  This causes the cells to die.  This triggers inflammation.  It also causes blood cells to begin to cling to the wall of the blood vessel and break down - that's the hemolysis bit - so you get a combination of kidney damage and blood cells breaking down, the hemolysis.  In a small minority of people, this can be sufficiently severe that they unfortunately die which is what we've seen in this time.  So it looks like it's a sort of mix and match between a form of the bug from overseas and some other forms of the bug which we know exist in nature.

Dave -   It seems a very specific piece of evolution to actually attack our kidneys in this way.  Is there any advantage to the bug? Killing its host seems like a really bad idea.

Cucumber fruitChris -   Well it's not universally fatal as you can see.  We think about 2,000 people have been infected with this new strain of E. coli since the outbreak began and interestingly, the outbreak we think now, there's some evidence emerged this evening, researchers are tying this to a festival that happened early in May - 6th, 7th of May in the Port of Hamburg.  They think that perhaps the mass gathering of people there, eating some kind of contaminated food stuff - probably salad vegetables, may have spawned the outbreak.  The reason that this bug is able to do this is that humans aren't the natural host of these organisms that cause this particular syndrome.  In fact, they probably come from farm animals.  Farm animals don't have the molecular target for the toxin that we do so they can carry these things perfectly harmlessly to them, and it comes out in their manure.  If you use that manure to fertilise your food crops, your salad vegetables, your tomatoes, and whatever to make them grow very well, the bugs that are carried can then get into the food.  One of the other things that stemmed from this piece of research being done in Beijing is that apart from being to make the toxins, this particular form of E. coli also has some genes that make it stick better to the cells of the intestine and possibly also to the cells in things like lettuce and tomatoes.  In other words, to survive better on those environments.  Because salad items aren't really cooked or boiled, usually raw, and as you peel the thing and peel the bug off the surface, then it's probably on the surface even in tiny numbers, and a small dose is an infectious does with this particular organism.

Chris, Dave and Dominic continued their discussion off air...

Dave -   So I guess this leaves on to the question which a lot of people have at home is - is there anything you can do to protect yourself?  Is it likely to be a major problem?

Chris -   Well we're probably seeing two phenomena at the moment.  The 2,000 or so people who have manifested it so far may either have been infected at the time the outbreak occurred - that will probably account for the bulk of them, and then there will also be some people who may have caught it from other people who've got it because the incubation period appears to be between 1 and 10 days.  So, people who were getting it may have got it and had a short incubation period, having got it off someone who has already got it, or they may just be a slow incubator, having had a smaller infectious dose, for instance, at the source.  At the moment, although it's spread to a number of countries in Europe in terms of numbers, all of those numbers appear to be connected to this particular geographical site in Germany.  So we think that's the source and we haven't seen onward spread - certainly not in the UK.  We haven't seen onward spread across Europe elsewhere, so it looks like it's being contained.  But obviously, this means people are going to have to be very vigilant and if people do get these kind of symptoms then they should go and seek help and also make sure that they are very careful with hygiene because it's a small infectious dose and it can spread on surfaces and things like that.

Dominic -   So would the bug be just on the surface of the vegetable or would it be spread through the whole flesh?

Chris -   I guess what you're asking is, peel it, boil it, or leave it - does this apply here?  The answer is that when the vegetables grow, the bugs can get onto the surface of the vegetable, and obviously, if we don't wash them properly then you could pick something up.  This is a frequent cause of travellers' diarrhoea when you visit third world countries.  People just eat things that haven't been washed properly.  But in certain circumstances, if there are small nooks and crannies on the surface of the vegetable, then the bugs can go into those.  In certain cases, the plant can then overgrow the bug, almost trapping the bacterium inside the plant's flesh and protecting it like a miniature capsule.  So that even if you do peel it, sometimes it's so deep into the flesh, you may not remove at all.  So, the answer is, probably, if you are thinking about being safe at the moment, you'd probably be wise to not consume vegetables brought from German markets in Hamburg.  As far as we know, there's no risk to people in this country at the moment and as I say, the numbers are not climbing dramatically anymore.  So we think it's probably okay.

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