1. Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine , Pittsburgh, Pennsylvania, USA
2. Department of Biological Sciences, Carnegie Mellon University , Pittsburgh, Pennsylvania, USA
3. Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania, USA
4. Department of Microbiology and Immunology, Emory University School of Medicine , Atlanta, Georgia, USA