Dangerous bacteria may be produced by antibiotic overuse
The discovery adds weight to warnings about inappropriate antibiotic prescribing - amid fears that overuse is helping the development of potentially dangerous "superbugs".
Doctors say that if antibiotics are misused, they may be unable to help when needed most, because bacteria have adapted to beat them.
The study, carried out in Canberra, Australia, tested 461 children aged under four, found pneumococcus bacteria - which can cause pneumonia - resistant to penicillin, one of the most commonly-used childhood antibiotics.
The authors are calling penicillin, and similar drugs, to be less frequently used.
Nasal swabs were taken every six months to check for the presence of bacteria.
The likelihood of carrying penicillin-resistant bacteria was doubled in children who had been given penicillin or a similar antibiotic in the previous two months.
Rising chance
In addition, for each additional day of antibiotic use over the previous six months, the chance of finding resistant bacteria was 4% higher.
"We found that 47% of all episodes of respiratory symptoms resulted in a visit to the general practitioner, and that up to 48% of children who visited their GP received an antibiotic on their first visit.
"The likelihood that antibiotic use will, in the short term, result in carriage of a resistant organism needs to be built into clinical decision making."
Restraint urged
A spokesman for the UK's Public Health Laboratory Service (PHLS) echoed this.
He said: "This research provides further evidence of just how important it is to ensure that antibiotics are used carefully and appropriately.
"If resistant bacteria get into a position where they cause
infection, they can be much more difficult to treat.
"This work reinforces the message that the more we use antibiotics, the more we promote the development of resistant bacteria."
Campaign started
The UK government launched its own campaign on Thursday to stop patients demanding antibiotics from their doctors - even for viral infections which will not be cured by them.
Deputy Chief Medical Officer Dr Pat Troop said: "Already some antibiotics are becoming less effective at fighting those infections and if we continue to use them inappropriately more bacteria will become resistant to them."
Drug resistant bacteria are a particular problem in hospitals, where it is estimated that they cost the NHS millions annually in extended hospital stays and extra treatment - and contribute to the deaths of thousands more.
Some bacterial strains have developed strong resistant to a whole series of antibiotic types as a result of exposure over long periods.
Resistance develops because the use of antibiotics naturally selects those strains which are best equipped to resist them - by killing the rest.