Now here's a smart way of shielding the body from harmful bacteria: use friendly microbes to do it for you.

Inflammation of the middle ear, otitis media, is a common and recurrent infection of children in the first few years of life. The standard treatment is to swallow large amounts of antibiotics. This costs money and promotes drug resistance. The alternative remedy, surgery, is expensive and not without risk. Clearly we need some help.

All microbes spend their short lives in a ceaseless Darwinian struggle for survival. The noses and throats of children who are prone to otitis media are known to harbour fewer of a particular group of benign streptococcal bacteria. It is assumed that these harmless microbes compete for living space with the less benign bacteria responsible for the disease. So, the fewer you have of the good guys the more you'll have of the bad - and vice versa.

You can guess what's coming.

Shift the bug balance in favour of the streptococci and you should improve things for the child in which they live. A group of Swedish doctors have now tested this neat idea, and their report in the BMJ (27 January) suggests that it works. They first dosed their subjects with one course of antibiotics to clear out all the bacteria, then administered a nasal spray containing either a culture of streptococci or a placebo solution. Three months later, twice as many of the children who had received the microbe-laden, as opposed to the microbe-free, spray had suffered no further problems.

As the authors say, most of the antibiotics used to treat otitis media kill not only those bacteria that cause it, but also those that would otherwise help to prevent it. In trying to solve the problem doctors may be simultaneously perpetuating it.

This column pointed out last time that increasing resistance dictates a more sparing use of antibiotics. How encouraging that such a clever contribution to reduced prescribing should turn up so speedily.