Methicillin-resistant staphylococcus aureus (MRSA) infections are caused by a type of staph bacteria that is resistant to the antibiotics commonly used to treat staph infections. MRSA skin and soft tissue infections can be treated with oral antibiotics that work against MRSA. These antibiotics include co-trimoxazole (trimethoprim/sulfamethoxazole), clindamycin or a tetracycline. If the infection is internal or doesn’t respond to oral antibiotics, you may need to be treated with intravenous (IV) antibiotics.