ON THE HORIZON

Readers may wonder whether a third mention of antibiotic resistance in this column in five months indicates an obsession. It doesn't. It reflects an encouraging interest by researchers in new ways of seeing off bugs.

Because bacteria are unicellular organisms, without a degree of mutual co-operation their capacity to influence circumstances is severely limited. One microbe mounting an assault on one cell of its human host would have about as much impact as a peashooter on a rhinoceros.

Rather than waste resources by behaving virulently when they have no chance of success, many bacteria do no real harm to their host until they have built up their numbers. Only then do they bother to act belligerently. This simple tactic requires them to know how many of them are present. Being simple souls, bacteria cannot count one another. They need some other means of sensing when they have the required quorum.

Their remedy is to release specific messenger molecules into their environment. Receptors on their surfaces respond to the concentration of these molecules around them - the more bacteria, the higher the concentration.

At a certain point, a change in behaviour is triggered.

I recently visited Nottingham University's institute of infections and immunity, where researchers have identified some of the molecules bacteria use for this 'quorum sensing'.

By developing chemicals to block the activity of the signalling molecules, researchers reckon they should be able to stop bacteria appreciating their own strength of numbers and behaving aggressively. Not so much attacking microbes, as taming them. Ingenious.