The MRSA can cause infection usually on skin and systemic infections when inhaled. If it infect the gum then there will be swelling and puss formation in the gum. It can be treated by lancing the blister first by the doctor and then use of antibiotics. If you are not having abscess or blister in mouth then it might not be MRSA. I advise you to get culture test to know the type of bacteria causing swelling of gums and then take antibiotics.