Comparison of the nucleotide sequence and expression of norA genes and microbial susceptibility in 21 strains of Staphylococcus aureus

The norA gene, which is located on the chromosome of Staphylococcus aureus, encodes the multidrug efflux protein with 12 transmembrane segments (TMS), and the overexpression of norA by the mutation of the transcriptional control region confers resistance to fluoroquinolones and antiseptics. In this study, the nucleotide sequence and transcriptional expression of norA genes were studied in six standard laboratory strains and 15 clinical isolates, which included 5 antiseptic-susceptible strains and 10 resistant strains. Seven mutations leading to up-regulation of norA transcription were identified. In addition, a novel allele of norA (norAII) was identified whose 3'-terminal region sequence and profile of antimicrobial susceptibility differs from those of original norA.