Why are antibiotics becoming less and less effective?

Resistant bacteria are not a recent problem. Antibiotics have existed for hundreds of millions of years as natural substances produced by micro-organisms, and in that time bacteria have already developed protective mechanisms. Human use over the past eighty years has enormously accelerated the spread of that resistance, but the foundation was already there.

How does that acceleration process work? Every time an antibiotic is used, the bacterium that happens to be better able to withstand it survives. That bacterium multiplies, and resistance increases. Researchers call this selective pressure. Overuse, misuse and overly liberal use in both humans and animals amplify that pressure. The result: resistant 'superbugs' are now commonplace in many countries.

Bacteria have four ways of outsmarting antibiotics. They can alter the target site so that the drug no longer fits. They actively pump the antibiotic out through pump mechanisms in the cell wall. They produce enzymes that break down the antibiotic, such as the enzyme that neutralises penicillin. And they make their outer layer less permeable. On top of that, they can sometimes form a slime layer inside which antibiotics have an even harder time getting through.

Particularly problematic is the fact that bacteria can pass resistance genes directly to one another, including to other species. This happens quickly and does not stop at national borders. Resistance genes are now turning up in aircraft wastewater, the faeces of migratory birds and ocean areas, so the spread occurs through all kinds of environmental routes. The WHO has designated six groups of bacteria as top priorities, including MRSA and Klebsiella pneumoniae, because infections caused by them are becoming increasingly difficult to treat.

Antibiotics also have a side effect that hits closer to home: they disrupt the body's own gut flora. Beneficial bacteria disappear along with the harmful ones. This can lead to diarrhoea, and with repeated use to persistent infections with a bacterium called Clostridioides difficile. There are also indications that early exposure in young children is associated with gastrointestinal and immune problems, although the causality for this is less certain.