Sunday, June 12, 2011

Bean Sprouts Bug has Plague DNA

The Hunt for the Source of Germany's E. Coli Outbreak:
The bacterium that is currently terrifying the country is an enterohemorrhagic strain of the bacterium Escherichia coli (EHEC), a close relative of harmless intestinal bacteria, but one that produces the dangerous Shiga toxin. All it takes is about 100 bacteria -- which isn't much in the world of bacteria, which are normally counted by the millions -- to become infected. After an incubation period of two to 10 days, patients experience watery or bloody diarrhea.
The bacterium in question was quickly found to be associated with vegetables grown close to the ground, which is unusual, since the majority of E. coli outbreaks are associated with meat or eggs.
The researchers sat patiently at the bedsides of those patients still in good enough condition to speak with them. Reconstructing all the meals they had eaten in the last few days wasn't easy. "It took hours," says Krause. But the researchers soon noticed something unusual: Hardly any of the patients had eaten raw meat or raw milk, the causes of almost all previous EHEC outbreaks, but almost all of them had eaten uncooked vegetables.

Could that have been the reason why the outbreak primarily affected women, at least at first? Had they become infected while chopping vegetables in the kitchen, or was it simply because women are healthier eaters?
I knew I had a good excuse for hating raw vegetables.  I just didn't know what it was.  Once the bacterium was cultured from the sick people it was determined that it was an unusual pathogenic strain.  However, the various articles I've seen disagree which one...  Most articles say 104:H4, some say 104:21 and at least one says 104:31.  Since none of us outside the microbiology profession know what those mean, it's probably irrelevant,but it is irritating that reporting can produce divergent answers...

Another interesting point is that the bacterium appears to share some DNA sequences with the bubonic plague, or black death:
On Tuesday, the German newspaper Süddeutsche Zeitung reported that Karch had discovered that the O104:H4 bacteria responsible for the current outbreak is a so-called chimera that contains genetic material from various E. coli bacteria. It also contains DNA sequences from plague bacteria, which makes it particularly pathogenic. There is no risk, however, that it could cause a form of plague, Karch emphasized in remarks to the newspaper.
Again; it's not really clear what's meant.  Most bacteria share have similar DNA for a fairly large number of genes that do similar things; the longer the species have been distinct, the more differences accumulate.  However, genes can jump between rather dissimilar bacteria through a process called conjugation.  Does this mean that this strain of E. coli has undergone recent conjugation with Yersinia pestis, the bacterium that causes the plague? Or do they think this is a "manufactured" bacterium; some really bad attempt at biological warfare?  Aaargghh.  Why can't journalists ask the right questions?

Anyway, the way the science seems to be shaping up now is that the contamination came from sewage waste used as fertilizer, before the land was planted.  Slugs apparently served as intermediate carries of the bacteria; their slimy coats providing the place where the bacteria survived until the plants present.  The bacteria has the unusual (at least in enterobacteria) ability to penetrate and grow beneath the surface layer of the plant, so that washing is unable to remove it.  At this point, apparently only bean sprouts have been directly linked to the bacterium and subsequent human infections, but that may change with further research.

So advice?  I don't really know.  While it's not happening in the US currently, it could.  Cook your vegetables I guess.  Now how do I tell Georgia that?

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