There are no ‘good’ or ‘bad’ microbes


Ed Yong writes: In the 1870s, German physician Robert Koch was trying to curtail an epidemic of anthrax that was sweeping local farm animals. Other scientists had seen a bacterium, Bacillus anthracis, in the victims’ tis­sues. Koch injected this microbe into a mouse – which died. He recovered it from the dead rodent and injected it into another one – which also died. Doggedly, he repeated this grim process for over 20 generations and the same thing happened every time. Koch had unequivocally shown that Bacillus anthracis caused anthrax.

This experiment, and those of contemporaries like Louis Pasteur, confirmed that many diseases are caused by microscopic organisms. Microbes, which had been largely neglected for a couple of centuries, were quickly cast as avatars of death. They were germs, pathogens, bringers of pestilence. Within two decades of Koch’s work on anthrax, he and many others had discovered that bacteria were also associated with leprosy, gonorrhoea, typhoid, tuberculosis, cholera, diphtheria, tetanus, and plague. Microbes became synonymous with squalor and sickness. They became foes for us to annihilate and repel.

Today, we know this view is wrong – as I explain in my new book I Contain Multitudes. Sure, some bacteria can cause disease, but they are in the minority. Most are harmless, and many are even beneficial. We now know that the trillions of microbes that share our bodies – the so-called microbiome – are an essential part of our lives. Far from making us sick, they can protect us from disease; they also help digest our food, train our immune system, and perhaps even influence our behaviour. These discoveries have shifted the narrative. Many people now see microbes as allies to be protected. Magazines regularly warn that antibiotics and sanitisers might be harming our health by destroying our microscopic support system. Slowly, the view that ‘all bacteria must be killed’ is giving ground to ‘bacteria are our friends and want to help us’.

The problem is that the latter view is just as wrong as the former. We cannot simply assume that a particular microbe is ‘good’ just because it lives inside us. There’s really no such thing as a ‘good microbe’ or a ‘bad microbe’. These broad-brush terms belong in children’s stories. They are ill-suited for describing the messy, fractious, contextual relationships of the natural world. [Continue reading…]

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