1. Department of Microbiology, University of Iowa, Iowa City, Iowa, USA
2. College of Public Health, University of Iowa, Iowa City, Iowa, USA
3. Carver College of Medicine, University of Iowa, Iowa City, Iowa, USA
4. Math and Science Division, Graceland University, Lamoni, Iowa, USA
5. Carleton College, Northfield, Minnesota, USA
6. Biology Department, University of North Carolina, Durham, North Carolina, USA