Speaking from an adult CFer's point of view, if they treated my staph (MRSA not MSSA) every time it showed up in a culture, I would never not be on antibiotics. Then, the bacteria would become resistant to the antibiotics. Unless your child's FEV1 is dropping or she is having other issues (coughing, SOB, etc.), it's better not to be given an antibiotic just because the staph is present in the culture.