1. Department of Biological Sciences, Northern Illinois University, DeKalb, IL 60115-2861, USA
2. Department of Microbiology, Molecular Biology and Biochemistry, University of Idaho, Moscow, ID 83844-3052, USA
3. Department of Biosciences and Pathobiology, Virginia Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0442, USA