Article  There is no such thing as a good or bad microbe (ethics community)

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EXCERPTS: . . . 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.

In reality, bacteria exist along a continuum of lifestyles. If they do us harm, we describe them as parasites or pathogens. If they exist neutrally, we call them commensals. If they benefit us, we bill them as mutualists. But these are hardly fixed categories. Some microbes can slide from one end of this parasite-mutualist spectrum to the other, depending on the strain and on the host they find themselves in. For example, the Wolbachia bacteria infect some 40 percent of insects; in some species, these microbes are sexual parasites that kill or manipulate males, whereas in others, they behave as living dietary supplements that provide vitamins missing from the host’s diet.

Other microbes can be pathogen and mutualist at the exact same time. The stomach bacterium Helicobacter pylori is well known as a cause of ulcers and stomach cancer. Less famously, it also protects against oesophageal cancer – and it’s the same strains that account for both these pros and cons. H. pylori is neither a good nor a bad microbe; it’s both.

All of this means that labels like mutualist, commensal, pathogen or parasite don’t work as definitive badges of identity. These terms are more like states of being, like hungry or awake or alive, or behaviours like cooperating or fighting. They are adjectives and verbs rather than nouns. They describe how two partners relate to one another at a given time and place.

[...] The important point here is that symbiotic microbes don’t come for free. Even when they help their hosts, they create vulnerabilities. They need to be fed, housed, and transmitted, all of which costs energy. And most important, like every other organism, they have their own interests – which often clash with those of their hosts...

[...] We like our black-and-white narratives, with clear heroes and villains. The very term symbiosis has been twisted so that its original, neutral meaning – ‘living together’ – has been infused with positive spin, and almost flaky connotations of cooperation and blissful harmony. But evolution doesn’t work that way. It doesn’t necessarily favour cooperation, even if that’s in everyone’s interests. And it saddles even the most harmonious relationships with conflict... (MORE - missing details)

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