Missing Microbes: How Killing Bacteria Creates Modern Plagues, by Martin Blaser

Stomach ulcers were long seen as the bane of the stressed, stewing in their own digestive juices. In the 1980s, it was discovered that Helicobacter pylori, a bacterium that can live in the mucus that lines the stomach wall, was invariably present in ulcerated stomachs. Cue a new, antibiotic-based cure for ulcers and a Nobel prize in 2005 for the two investigators who did most to make it possible. The finding that the same bug increases the risk of stomach cancer confirmed its reputation as a pathogen, and “the only good H. pylori is a dead one” became conventional wisdom.

But not for long. Martin Blaser, originally an infectious disease specialist, has examined the relationship between this organism and its human hosts in detail, and concludes that it is more complicated. Sometimes it causes harm, but its presence may also be part of normal human development. Lose it, and you may escape ulcers but are more likely to suffer heartburn and asthma.

And lose it millions of us have, not by intent but because of the wider use of antibiotics. Blaser’s work suggests that most people born in the US in the early 20th century harboured the organism, but only 6 per cent of children born after 1995 have it.

The finding takes on wider significance, he argues, as we ponder the effects of the complete human microbiota – the trillions of microbes on our bodies and in our guts that advances in DNA technology show to be far more diverse than we suspected. Their cells may outnumber our own tenfold, but their genes by two orders of magnitude more.

We co-evolved with these fellow travellers, and they are important in digestion and, in ways we are just beginning to unravel, in regulating the development and reactions of our immune systems. Assaulting them repeatedly with antibiotics, as routine medical practice tends to do, depletes them, and lays us open to unforeseen consequences. Those consequences, Blaser suggests, include a raft of chronic conditions that are on the rise – including obesity, food allergies, asthma and maybe even autism.

The links between those problems and changes in the microbial communities people have carried with them throughout history certainly bear investigation. Blaser details experiments that have begun to show some of the mechanisms that may be in play, most of them turning on the balance between inflammatory and anti-inflammatory signals in the lower portion of the gut, perhaps the densest and most complex ecosystem on the planet.

Some links remain speculative, and Blaser is clear when that’s the case. He is also cogent on his main subtheme, the overuse of antibiotics, even though his suggestions about “extinction of the microbiome” in recent interviews are overblown. There is a lot more of the story of the modern microbiota to come out, but it is already clear that it provides new reasons why overprescribing antibiotics is unwise. Feeding subclinical doses to livestock because it makes them gain weight faster is simply crazy, not least because it promotes resistance to the drugs. It is already banned in the European Union, and since Blaser finished writing this book the US has taken the first real steps to eliminate its use. Now to get to work on the doctors.