To me it sounds like you dont even have your story straight - a dog bite gave some one mersa?
James Ruby
Actually, it's MRSA or methcillin resistant staphlococcus aureus. It's a very drug resistant common variant of a normal bacteria that everyone probably has. There is community acquired CA-MRSA that can be treated fairly well with some run of the mill antibiotics and there is the healthcare facility MRSA that can be a big time concern.
Dogs have dirty mouths. Every mouth of every animal is relatively dirty from a bacterial perspective. At any rate add in whatever is in the dog slobber plus whatever bacteria are on the skin of the victim and then puncture the skin and push those bacteria into what amounts to the best petri dish ever and "ta da" you get a nasty infection.
Some are blamming the medical personell for the infection stuff but sometimes it's nobody's fault. Sometimes it's just bad luck.