1. Institute of Biosciences and Technology, Texas Medical Center, 2121 West Holcombe Boulevard, Houston, TX 77030-3303, USA1
2. Department of Microbiology, Moyne Institute of Preventive Medicine, Trinity College, Dublin 2, Ireland2
3. EA1655, Faculté Laennec, 69372 Lyon Cedex 08, France3
4. Department of Biochemistry, University of Pavia, 27100 Pavia, Italy4