A Spoonful of sugar helps the medicine go down
The medicine go down-wown
The medicine go down
Just a spoonful of sugar helps the medicine go down
In a most delightful way
We've all heard the song "A Spoonful of Sugar" from the movie "Mary Poppins." Now replace the word "medicine" with "E. coli" and you've got an entirely different song and idea altogether. A team of researchers from Australia and the US worked together to discover that an endogenous sugar in red meat and dairy products may promote binding of toxins produced by E. coli bacteria. Now before you go giving up your milk and meat, calm down...this study is not a cause for alarm, but it certainly provides those who shun consumption of bovine products more evidence for why eating beef isn't quite as good for you as you think. Or does it?
The sugar in question is what is known as a sialic acid N-glycolylneuraminic acid (say that 3 times fast!), which is present in most mammals...except, guess who? Yep, humans. It seems that quite a long time ago, in our early evolutionary history, because of a mutation, we lost the ability to produce this sugar which resides on the outer surface of mammalian cell membranes. Instead, we produce its analog, Neu5Ac. The significance of this sugar is that it belongs to a group of compounds known as glycoproteins which serve as identifiers on the outside of our cell membranes. They are key in stimulating an immune response against foreign cells (like bacteria, viruses and cancer cells), but also in aiding our own immune system to prevent it from attacking us inadvertently. Apparently, the mutation happened right before our common ancestor with other primates appeared and so we do not produce this particular sugar. However, other mammals like cows (the source of many an ice cream shake or tasty hamburger) retained the ability to produce this sugar as the gene responsible for its production has been well-conserved over time. It should be noted that the Neu5Ac also allows for us to be resistant to a strain of Plasmodium that causes malaria in other animals, but makes us susceptible to other Plasmodium species that cause malaria in humans.
Now what does this sugar have to do with E. coli? Bear in mind that the E. coli the authors are looking at are what we call Shiga-producing E. coli; in other words, they produce Shiga toxin, which is extremely harmful to the gastrointestinal system of humans and has been known to cause death. One researcher, Andy Benson of the University of Nebraska states: “Now you’ve got a scenario where the organism — the toxin — actually needs something from the food it’s carried in — that’s truly unique.” It is rather interesting that in this particular case, the toxin produced by the bacteria requires something to activate it, rather than the bacteria requiring something to activate it to produce the toxin itself. Could this be a form of molecular coevolution? And if it is, why hasn't it happened this way for other toxins produced by bacteria? If this is a form of molecular coevolution, how did selection occur at the molecular level so that this toxin could bind to this particular sugar and not some other?
Now does this mean you need to give up that burger and milkshake? No. But it does raise some interesting issues. Many countries around the globe consume beef products in large quantities, and many people raise cattle as a livelihood. Could this spell the end of ranching and cattle-raising as we know it? Or will it lead scientists to find ways to possibly genetically modify and then selectively breed cows so that they no longer produce this sugar on their cell membranes? What would the ethical implications be of such an action? What would the ethical implications be if no action were taken?
Posted by scienceguru on November 2, 2008
Tags better living through biological science, bioethics, dilemmas dilemmas!, discuss, evolution, science and society, what do you think?


Comments on specific paragraphs:
Click the
icon to the right of a paragraph
Comments on the page as a whole:
Click the
icon to the right of the page title (works the same as paragraphs)