Humans are surrounded by microorganisms: viruses, bacteria, fungi and parasites. We can divide these organisms into the following four categories: innocent, beneficial, harmful and dangerous. Most of the times, microorganisms are not harmful and are therefore referred to as non-pathogenic. Innocent microorganisms cause no harm nor do they provide benefits. Benefi cial microorganisms even provide a significant advantage for humans by aiding digestion or preventing pathogenic microorganisms to cause infection via colonisation resistance. By colonising the respiratory and/or gastro-intestinal tract, these organisms prevent pathogenic microorganisms to settle and cause harm. Pathogens causing harm in certain cases, but not per definition, are grouped into the harmful category. However, microbes that fall into the dangerous category comprise organisms that cause morbidity and mortality in humans even in those with an intact immune system.

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A.F. van Belkum (Alex) , H.A. Moll (Henriëtte)
Erasmus University Rotterdam
The first phase of the Generation R Study was made possible by financial support from the Erasmus Medical Center, Rotterdam, the Erasmus University Rotterdam and the Netherlands Organization for Health Research and Development (ZonMW). Additionally, an unrestricted grant from the European Container Terminal (ECT) - Rotterdam funded this project. The printing of this thesis has been financially supported by the Erasmus University Rotterdam and The Generation R Study Group, Rotterdam. Further financial support for this dissertation was kindly provided by: J.E. Jurriaanse Stichting, Stichting Astma Bestrijding, Merck Sharp & Dohme BV, Danone Research – Centre for Specialised Nutrition, Luminex BV, Abbott BV, Sanofi Pasteur MSD and GlaxoSmithKline BV.
hdl.handle.net/1765/22727
Erasmus MC: University Medical Center Rotterdam

Lebon, A. (2011, March 16). Bacterial Colonisation of the Nasal and Nasopharyngeal Cavities in Children: The Generation R Study. Retrieved from http://hdl.handle.net/1765/22727