Question: what percentage of bacteria on average is good

Clare Taylor answered on 12 Nov 2012:

That is a great question, and also a difficult one to answer! It depends on what you mean by ‘good.’ I have seen some estimates that around 30% of bacteria are bad (i.e. they can cause disease), so that would mean that the remaining 70% of bacteria are non-harmful but would we say that they are they all good? Well, it would depend on where the bacteria are and what they are doing. Let me use an example – a bacterium called Pseudomonas fluorescens causes food spoilage – it makes food rot and smell really bad. Now we might think that is bad because our food goes off, but think about how much waste food would cover the earth if bacteria and other microbes called fungi didn’t break it all down and help it to rot… Think about what happens in a compost heap – you put lots of stuff in but after a few weeks, the bacteria and fungi break it all down and the physical mass actually gets smaller. If the bacteria didn’t do this, we’d all be surrounded by piles of waste!

If we use the human body as a different example, there are literally millions and millions of bacteria inside us, most of which are ‘good’ because they help us to digest food and some even make vitamins, but importantly they help to keep us safe from bad bacteria because they can out-compete bad bacteria in the body. But occasionally, even some of these ‘good’ ones can become bad.

Other bacteria we call ‘good’ because we use them for beneficial purposes like making cheese, yoghurt and all sorts of things that we use in our every day lives. So although I can’t say for sure how many are ‘good’ I can definitely say that there are more ‘good’ then bad!