1. Division of Inhalation Toxicology, Institute of Environmental Medicine, Karolinska Institutet, SE-171 77 Stockholm;
2. Division of Clinical and Oral Bacteriology, Department of Immunology, Microbiology, Pathology and Infectious Diseases, Huddinge University Hospital, SE-141 86 Huddinge, Sweden; and
3. Faculty of Microbiology, University of Costa Rica, San Juan, Costa Rica