Are there any antibiotics that the patient is taking when cultured for MRSA that would give a negative MRSA result in the lab but a positive result when cultured 48 hours post treatment? In other words can certain antibiotics suppress the growth without eradicating the bacteria.
Certainly antibiotics can have an effect on MRSA that does not necessarily eradicate colonization. In fact, most systemic (oral or IV) therapy does not eradicate colonization – that is precisely why decolonization regimens include topical agents. However, antibiotics may have an effect on screening cultures and, in general, screening cultures should not be done while on antibiotics. Most people advise being off of antibiotics for > 1 week before doing screening cultures for colonization.