Once a person is infected with the mrsa infection and is treated, does that bacteria stays in the body forever?

Sometimes: Sometimes, if your immunity is low, you may harbor MRSA especially in the nasal cavity. Then you are called a carrier of the infection. Usually it can be treated with Mupirocin ointment.

Yes and no.: Some people become a carrier of MRSA and it stays in nose and fingernails forever. Incidence of this is 1-2%. Once you are treated it may or may not show up ever, 99% of time first MRSA infection is completely cured. If you get recurrent MRSA infection have your physician swab your nasal cavity to rule out carrier state.