Stefan Janusz reports :: February 2008

Bacteria that exhibit resistance to antibiotics are the stuff of nightmares for both patients and clinicians. Are we using too many antibiotics unnecessarily? And what about the requirement to properly finish a course of antibiotics? Many of us know that we should, but why exactly? And just how are these little ‘bugs’ evolving resistance so quickly?

It turns out that bacteria adapt to antibiotics more quickly than can be accounted for by mutations – minute random alterations to the DNA sequence – alone. Stable mutations can arise, but the numbers are low: at most, about one in a million bacteria become resistant. A team at the Children’s Hospital Research Foundation in Cincinnati, Ohio have reported that bacteria exposed to low levels of antibiotic have a survival rate of 1 in 5, and what’s more, the next generation have a survival rate of 1 in 2, which suggests that an epigenetic survival mechanism is in play. But how do the researchers know that it could be epigenetic? It turns out that, although the resistance trait can be passed on, it is easily lost, whereas for a change made to the DNA sequence to revert back to the original state is an extremely unlikely event – with a chance of about 1 in a billion – making an epigenetic process the likely explanation.

Why should we finish our course of antibiotics? Because epigenetically-altered bacteria are slippery customers.