The best test to confirm presence of MRSA is a bacterial culture. Pus is taken from skin sores and rubbed onto agar (a stiff gelatin-like substance in petri dishes). If bacteria are present, they will grow. Then chemical tests are done to see if MRSA is present. This type of testing, called a bacterial culture, takes about 2-5 days to perform. This type of test needs to be performed through a medical professional.