You might be tracking in more than mud on those shoes. A study released by Dr. Charles Gerba, a microbiologist and professor at the University of Arizona, and The Rockport Company found large numbers of bacteria on the bottom and inside of shoes. Shoes in the study averaged 421,000 units of bacteria on the outside and 2,887 on the inside. Some of the bacteria found included Escherichia coli, known to cause intestinal and urinary tract infections, meningitis and diarrheal disease; Klebsiella p...