1. A. J. Bäumler is in the Department of Medical Microbiology and Immunology, College of Medicine, Texas A&M University Health Science Center, 407 Reynolds Medical Building, College Station, TX 77843-1114, USA.
2. B. M. Hargis and R. M. Tsolis are in the Department of Veterinary Pathobiology, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843-4467, USA.and