Question: is unhealthy bacteria good or bad for you

Jim Caryl answered on 23 Jun 2011:

Well, when I describe bacteria as being ‘unhealthy’, what I mean is that they are less ‘fit’ than a similar bacteria when gown in a particular condition. So my idea for the gene gym is to add a single gene to one strain of bacteria, which makes it able to resist antibiotic medicine that would normally kill it, or stop it from growing. I then compete this bacteria with an almost identical strain that doesn’t have that extra gene in it.

In the presence of antibiotic, obviously the one with the extra gene is going to do better. However, if we take the antibiotic away, which strain will do better, the one with the extra gene, or the one without? This is the question I’m testing.

Sometimes having an extra gene puts a ‘metabolic load’ on the cell, making it have to do more work and expend more energy. If you likened having that extra ‘defence’ gene to you wearing a suit of armour – the armour will be great if people are throwing stones at you, but if no-one is throwing stones, it’s just a very heavy thing to carry around – so in this way, I would say that adding this gene makes the bacteria ‘unhealthy’.

Just because a bacteria is ‘unhealthy’, doesn’t mean it’s any more or less likely to cause disease, it’s just less likely to than a related bacteria that doesn’t have the gene. The defence gene will make the antibiotic medicine useless, so we can’t use it to treat people with infections caused by that bacteria any more, which is bad.

What IS important however, is that if we know that the particular defence gene makes the bacteria unfit, then there is a good chance it won’t stick around. So if we were to stop using the particualr antibiotic medicine that the gene defends against, that gene may vanish from the bacterial population and we would be able to one day start using that medicine again.

However, some antibiotic defence genes are carried by bacteria with no problems whatsoever, and even if we stopped using antibiotic medicine to treat them, they would still hang on to this gene. I’d like to know which types of antibiotic defence genes do this too.