Beating Cholera with Sugar

Cholera is a horrible disease caused by infection by a type of bacteria called Vibrio cholera. It causes severe diarrhoea and vomiting. Without any treatment people can die very quickly from dehydration. This is worst in undeveloped countries or cases of natural disaster, where water supplies can be dirty and the bacteria can spread easily. For example, in October 2016 Hurricane Matthew swept through Haiti, filling their wells with diseased water and spreading cholera.

vibrio cholera bacteria disease sugar gut intestine

Scanning electron micrograph of Vibrio cholera. Credit: http://dx.doi.org/10.1046/j.1365-2958.2000.01764.x

There are treatments of course. Normally patients take electrolyte solutions to rehydrate them and they take antibiotics to kill the bacteria. This isn’t always available to everyone, especially during times of crisis.

There is also a bigger problem that we are starting to face. Antibiotic resistance. Some bacteria have learnt how to defend themselves from antibiotics, which makes the treatment ineffective.

So how will we treat cholera in the future? One answer might be sugars. To learn why this is we first need to know how cholera infection works.

Steps in cholera infection

When a person drinks dirty water containing cholera, the bacteria get to the gut and start to grow.

Human cells on the gut lining are covered in a sugar called GM1.

The bacteria release a toxin that sticks to GM1, causing the human cell to swallow the toxin.

Once inside, the toxin switches on a pump that causes salt and water to pour out of the cell and into the gut.

Some of the cholera gets washed out in the diarrhoea and vomit. If anyone else gets into contact with this, they will get infected too.

cholera mechansim gm1 toxin chloride sodium salt water gut infection

Cholera Infection. The toxin sticks to a sugar called GM1, which causes water and salt to be pumped into the gut. Credit: http://dx.doi.org/10.1016/j.tips.2005.02.003

Beating Cholera with Sugar

Since the symptoms of cholera are caused by the toxin getting inside human cells, the disease can be treated by stopping this from happening. One way that scientists are trying to do this is by making drugs that look the same as GM1. That way the toxin will stick to the drug instead of GM1, stopping the infection.

One problem with using polysaccharides (that means lots of simple sugars stuck together – I wrote a post about that here) like GM1 as drugs is that the oxygen bonds are quite easily broken, so the drug could fall apart before it gets to the cholera. This problem can be fixed though by replacing the oxygen with another element called sulphur. Sulphur behaves very similarly to oxygen, except that it is a bit bigger and less reactive, which makes the drugs more effective.

Another problem is that big sugars like GM1 are difficult to make artificially because they are very complex. Luckily we know which part of GM1 are the most important for sticking to cholera toxin. It’s the galactose and sialic acid sugars at the end of each branch.

Scientists are working on making drugs that link these two sugars together in a way that tricks cholera toxin into thinking that it is GM1. Hopefully in the near future this will be an effective treatment for cholera and will save thousands of lives. Go sugar!

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