What gram-positive bacteria grows in chains and acts like mrsa? why would somebody infected with this bacteria need to have their limb amputated?

I : I think you may be referring to streptococcus pyogenes which has been dubbed the "flesh-eating bacteria" by the media. This bacteria can cause necrotizing fasciitis which is a potentially deadly disease. The bacteria enters the skin through a small cut and rapidly starts destroying soft tissues such as muscle, skin, and blood vessels. Treatment requires powerful antibiotics and surgery to remove the dead, infected tissue. In cases where the infection in an arm or leg cannot be controlled, amputation is considered in order to save the person's life. I added a link below with more information on strep pyogenes and necrotizing fasciitis.

Strep. pyogenes: Group a beta hemolytic streptococci or streptococcus pyogenes is a common cause of necrotizing fasciitis "flesh eating bug" infection. The treatment involves debridement of all necrotic fascia and other necrotic soft tissue and sometimes requires limb amputation.