Problem: MRSA, or Methicillin-resistant Staphylococcus aureus, has become an important challenge in the medical community. As mentioned in the text, today more than 90% of S. aureus strains are resistant to penicillin. Explain what led to this level of antibiotic resistance (biologically, what occurred), why it is concerning, and what options are available for individuals who become infected with S. aureus.