1. Institute of Hygiene, University Hospital Münster, Germany
2. Institute for Health and Work (LIGA) North Rhine-Westfalia, Münster, Germany
3. Faculty of Behavioural Sciences, University of Twente, Enschede, the Netherlands
4. Policlinics of Periodontology, University Hospital Münster, Germany
5. Institute of Medical Microbiology, University Hospital Münster, Germany
6. Laboratorium Microbiologie Twente-Achterhoeck, Enschede, the Netherlands