Question: Why is it that some bacteria can make you sick but some can help your bowel ??

Kevin Lomasney answered on 15 Nov 2012:

Hi jf4567,

Well, bacteria are like animals and humans. There are all different kinds. Some are dangerous and are only out for their own gain, like predatory animals they are only interested in their own survival. These kind of bacteria are known as pathogenic bacteria Other bacteria prefer to work together with another organism and live in what’s called a symbiotic relationship where both organisms benefit and survive very well. These are known as commensal bacteria and there are more of these in your bowel than cells in your body! They help us digest a lot of different nutrients and also protect us from bad bacteria. In return we give them a place to live (though it doesn’t seem like the nicest house in the world) and they also feed from the food we take in.

The most important difference between the harmful pathogenic bacteria and the friendly commensal bacteria is the presence of what’s of virulence factors on the pathogenic bacteria. These virulence factors are like weapons which allow the pathogenic bacteria to attack and invade another organisms, as well as kill other bacteria. For example, bacteria such as E. coli or Salmonella, can attach to your bowel cells and inject chemicals which causes your bowels to expel a lot of water. This is why we get diarrhea if we have been infected by these bacteria. Ever hear of Cholera? It is one of the biggest killers of people in the third world (millions each year) and it kills these people by giving them severe diarrhea which makes them dehydrated because of all the water lost. Its really horrible, and guess what causes it, a bacteria, Vibrio cholera. It has a virulence factor which allows it to produce its toxin (cholera toxin) which causes the diarrhea in a similar but slightly different manner to E. coli.

The worst thing is that there is no medicine currently to cure these people and so it continues to kill millions. Instead people take a mixture of sugar and water to help rehydrate them. However, there is a chance that using the good bacteria may a new way to treat these people. When you use commensal bacteria to treat a disease (or just to improve your health), they are called probiotics. These good bacteria do not have virulence factors because thoughout evolution they have adapted to living in unison with other organisms. However they do have some tools to ensure their survival and also protect us at the same time. For example, one of these good bacteria can produce a chemical which can kill harmful invading bacteria but not itself or other good bacteria! There is also a probiotic which can block the cholera toxin and prevent it from causing diarrhea.

However, there is still much work to be done as these probiotics unfortunately are not always effective. If we can figure out exactly how they are working then perhaps we can make them more effective and find real cures for people like those in third world countries.