1. Research Institute of Biomedical Sciences, Department of Medical Clinics, University Center for Health Sciences, University of Guadalajara, Guadalajara, Jalisco 44340, M�xico
2. Department of Microbiology and Pathology, University Center for Health Sciences, University of Guadalajara, Guadalajara, Jalisco 44340, M�xico
3. Department of Otorhinolaryngology, West National Medical Center, Mexican Institute of Social Security, Guadalajara, Jalisco 44340, M�xico
4. Department of Physiology, University Center for Health Sciences, University of Guadalajara, Guadalajara, Jalisco 44340, M�xico