29 October, 2008
Evolution is a cruel mistress. Since the 1940s millions of people have had their lives saved and immeasurably improved by the use of antibiotics. Bacterial infection weakens and kills us, and until antibiotics came along fresh air and rest were often the only prescription that doctors could give. All of us are covered and filled with bacteria, but these are mostly symbiotic in nature, we use them as much as we use our own cells to function. But those bacteria which harm us have to be dealt with, and with something more subtle than bleach. Sure we have chemicals that kill almost everything they touch, but unfortunately that means we can’t take them inside our bodies to help fight the bacteria harming us. To do that we use antibiotics, special chemicals that target the specific types of bacteria we want to get rid of.
Some antibiotics kill bacteria. They explode the cell wall and leave nothing functioning behind. Other antibiotics prevent bacteria from multiplying. The bacterium grows and grows but cannot divide and so is restricted in its ability to harm us. In each case we stop the bacteria but introduce a powerful natural selector. Any strain of bacteria that has resistance to the antibiotic will thrive, it will have no competition from its siblings who are dying or being prevented from reproducing. In the sixty or so years since antibiotics started to be used on a mass scale bacteria have evolved which are resistant to almost all of our drugs. With some, such as MRSA, anyone found infected with it is put onto the ‘drug of last choice’ – the only known antibiotic with some effectiveness against it. It is only a matter of time before we inadvertently breed resistance against this drug too.
So is it time to invest a lot of money in more of these antibiotics? Very few companies seem willing. With a development time of a decade, and hundreds of millions of euros spent on clinical trials, companies like to see a profit returned in the first ten years or so of a drug being put out onto market. Unfortunately most new antibiotics have a shelf life of only a few years before resistance crops up again. It’s unprofitable and fighting against an enemy that moves faster than we can. So what’s the solution?
One possible way forward has been revealed by luminescent bacteria. Several types of sea creatures hold glowing bacteria in translucent pouches which are used as lures, or signalling devices. But some types of these bacteria have an interesting property. Looking at a few of them under a microscope and you wouldn’t see any glow. But put enough of them together and they start to emit light. This is known as quorum sensing, the bacteria emit chemical signals and when they receive enough of them back they know it’s worth their while to perform some operation – in this case to shine.
Quorum sensing has since been found in other bacteria, but this time the bacteria wait until there is a large enough group before turning virulent. It makes sense for the bacteria not to alert a bodies defence mechanisms until it has a good chance of surviving, and those large numbers make it easier to survive. And so a possible solution to the problem of evolving bacteria presents itself. If drugs can be developed that stop the quorum sensing chemicals from being released, or from being detected, then the bacteria will happily grow without ever turning nasty. In this way, rather than the hammer of death leading to new strains, the original strains will still be around, but rendered harmless.
We are some way from seeing if this idea will work in practice, but unless some new ideas come to the table our short but highly successful victory over many kinds of disease will soon be coming to an end.