1. Department of Pathology, Stanford University School of Medicine, 300 Pasteur Drive, Stanford, CA 94305–5324, USA.
2. Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA 94305–5124, USA.
3. Stanford University High-Throughput Bioscience Center, 1291 Welch Road, Stanford, CA 94305–5174, USA.
4. Division of Infectious Diseases and Geographic Medicine, Department of Medicine, Stanford University School of Medicine, Stanford, CA 94305–5107, USA.
5. Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, VT 05405, USA.