Culture is the most widely used test to identify colonization of MRSA. This type of exam confirms the presence of the resistant, but culture takes time, usually about 48 hours. A nasal swab is collected from the nostrils of an asymptomatic person and cultured (put onto a special nutrient medium,incubated,and then examined for the growth of characteristic Methicilin resistant Staphylococcus Aureus colonies). Also, a swab can be collected from a skin lesion or wound site of a patient who has been previously treated for a MRSA and cultured similarly.

Latest modern and significantly faster method of testing Methicilin resistant Staphylococccus Aureus by molecular method have been developed. Aim of these methods examines for the mecA gene that confers immunity to the antibiotic methicilin,nafcilin,oxacilin and dicloxacilin and some other type of similar antibiotics. This molecular exams for MRSA have potential to detect nasal or wound carriage within hours instead of 1-2 days required by culture MRSA tests.
http://www.mrsaskininfection.org/mrsadiagnosisandtesting.html
http://www.staph-infection-resources.com/articles/mrsa_tests_and_getting_a_correct_mrsa_diagnosis.html