Cloning and expression of the norA gene for fluoroquinolone resistance in Staphylococcus aureus

The norA gene for fluoroquinolone resistance in Staphylococcus aureus TK2566 was cloned from chromosomal DNA into fluoroquinolone-susceptible Escherichia coli TG1. The resulting transformant, NY11, contained a recombinant plasmid, designated pTUS1, with a cloned 5.5-kilobase (kb) HindIII fragment of staphylococcal DNA. The MIC of norfloxacin for the strain increased from 0.1 to 3.13 micrograms/ml. Furthermore, when the fragment was recloned into S. aureus, the transformant NY12, containing recombinant plasmid pTUS20, had the same level of resistance to norfloxacin as did the original strain, although it was less resistant to ofloxacin and ciprofloxacin. A single KpnI-HaeIII fragment was found to be the minimum size able to express norfloxacin resistance, suggesting that the norA gene is located within the 2.6- to 3.2-kb region of the original 5.5-kb fragment. The 5.5-kb fragment hybridized to DNA from a fluoroquinolone-susceptible S. aureus strain.