Should i be concerned if my 75 year old grandma has a colon infection how does this occur what causes it?

Depends: Is is clostridium difficile? This is an infection that can occur after antibitoic treatment for any other infections and is not uncommon in the elderly. I can however, become a significant problem and be difficult to eradicate. It also can be transmitted to others that have a weak immune system. Antibiotics include Metronidazole and/or vancomycin. Newer antibiotics have been developed as well.