Effect of the repeated use of antibiotics

Antibiotics are drugs which are used every day for plenty of diseases. Doctors are encouraged to use them carefully. The use of antibiotics is one of few situations when the condition of the patient is not always in the first place, because the condition of the whole population is almost this important. Everybody knows what the resistance to several antibiotics can cause. But what do we know about the hidden effects on the intestinal bacterial flora? American scientists (Relman et al., 2010) decided to face this question and find out more.

The repeated use of a well tolerated antibiotic is considered not to cause problems, because patients rarely suffer from evident side effects. However the research performed by experts at Stanford University School of Medicine (Relman et al. 2010) revealed that it induces cumulative and persistent changes in the composition of bacterial flora. It is estimated that thousand different types of microorganism live in the human gut playing important roles.

The study was led by David Relman and was published in Proceedings of the National Academy of Sciences (Relman et al. 2010). It examined the effects of ciprofloxacin, an antibiotic often prescribed in the case of many infections, particularly intestinal and urinary ones. The drug rarely gives side effects such as diarrhea or abdominal swelling. Using new analytical techniques for studying the bacterial flora, the researchers examined the effects of two treatment cycles of five days led in a six months distance. The scientists detected a small long-term effect: the substitution of different bacterial species with other residents, but also the complete disappearance of others.

The general similarity between the strains which were present before and after the treatment explains according to the authors (Relman et al. 2010) the low incidence of side effects of ciprofloxacin. „However, the bacterial strain which disappeard could have an important biological function, such as production of a protein which is toxic to specific pathogens. So this function is lost," noted Relman. This function might have not be used for years, but can become important when the relevant pathogen invades the intestine of the patient.

"This does not mean that these or other antibiotics are dangerous or should be avoided," explained Relman. „But our findings raise again the question of their effective use and the possible long term side effects." Even more important would be a further research of the specific functions performed by different types of bacteria, even if the task is very complex, because the specific bacterial composition varies from person to person.

If we managed to do that, thanks to the new technique for the identification of intestinal bacteria strains, we would think of evaluating the presence of species that make up the intestinal flora before and after the antibiotic treatment. This would help us to administer specific probiotics that promote the recovery of the strains in danger.

Translated by Pavla Čermáková

Story source: http://lescienze.espresso.repubblica.it/

Original work: Les Dethlefsen, David A. Relman: Incomplete recovery and individualized responses of the human distal gut microbiota to repeated antibiotic perturbation, August 2010

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