Development of resistance to ciprofloxacin, rifampin, and mupirocin in methicillin-susceptible and -resistant Staphylococcus aureus isolates

A relationship between resistance to methicillin and resistance to fluoroqu inolones, rifampin, and mupirocin has been described for Staphylococcus aur eus. Differences in resistance rates may be explainable by a higher spontan eous mutation rate (MR) or a faster development of resistance (DIFF) in met hicillin-resistant S. aureus (MRSA). No differences in MR, DIFF, and mutati ons in grlA. and gyrA were detected between methicillin-susceptible S. aure us and MRSA. The higher resistance rates in MRSA are not the result of hype rmutability of target genes or a faster emergence of different mutations an d may be the consequence of clonal spread of multiresistant MRSA.