1. School of Dental Sciences, University of Liverpool, Daulby Street, Liverpool L69 3GN, U.K.
2. Department of Microbiology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, ul. Gronostajowa 7, 30-387 Krakow, Poland
3. Department of Periodontics, University of Louisville School of Dentistry, Louisville, KY 40202, U.S.A.