Explain the progression of disease that begins with the action of Streptococcus mutans and ends with periodontal disease. Why do bulimics often have highly damaged teeth? Explain the process that leads to the formation of a peptic ulcer. How does this contrast with beliefs regarding the cause of ulcers that were widely held before 1980. Why is infection with Shigella dysenteriae considered to be far worse than infection with other members of this genus? Explain the action of shiga toxin and shiga-like toxin..