Kaatz G W, Seo S M, Ruble C A
Department of Internal Medicine, Wayne State University School of Medicine, Detroit, Michigan 48201.
Antimicrob Agents Chemother. 1993 May;37(5):1086-94. doi: 10.1128/AAC.37.5.1086.
Transport processes are used by all organisms to obtain essential nutrients and to expel wastes and other potentially harmful substances from cells. Such processes are important means by which resistance to selected antimicrobial agents in bacteria is achieved. The recently described Staphylococcus aureus norA gene encodes a membrane-associated protein that mediates active efflux of fluoroquinolones from cells. SA-1199B is a fluoroquinolone-resistant strain of S. aureus from which we cloned an allele of norA (norA1199). Similar to that of norA, the protein product of norA1199 preferentially mediates efflux of hydrophilic fluoroquinolones in both S. aureus and an Escherichia coli host, a process driven by the proton motive force. Determination of the nucleotide sequence of norA1199 revealed an encoded 388-amino-acid hydrophobic polypeptide 95% homologous with the norA-encoded protein. Significant homology with other proteins involved in transport processes also exists, but especially with tetracycline efflux proteins and with the Bacillus subtilis Bmr protein that mediates active efflux of structurally unrelated compounds, including fluoroquinolones. In S. aureus, the norA1199-encoded protein also appears to function as a multidrug efflux transporter. Southern hybridization studies indicated that norA1199 (or an allele of it) is a naturally occurring S. aureus gene and that related sequences are present in the S. epidermidis genome. The nucleotide sequence of the wild-type allele of norA1199, cloned from the fluoroquinolone-susceptible parent strain of SA-1199B, did not differ from that of norA1199 throughout the coding region. Northern (RNA) and Southern hybridization studies showed that increased transcription, and not gene amplification, of norA1199 is the basis for fluoroquinolone resistance in SA-1199B.
所有生物体都利用转运过程来获取必需营养物质，并从细胞中排出废物和其他潜在有害物质。这些过程是细菌对特定抗菌剂产生耐药性的重要方式。最近描述的金黄色葡萄球菌norA基因编码一种与膜相关的蛋白质，该蛋白质介导氟喹诺酮类药物从细胞中主动外排。SA - 1199B是一株耐氟喹诺酮类药物的金黄色葡萄球菌菌株，我们从该菌株中克隆了norA的一个等位基因（norA1199）。与norA相似，norA1199的蛋白质产物在金黄色葡萄球菌和大肠杆菌宿主中均优先介导亲水性氟喹诺酮类药物的外排，这一过程由质子动力驱动。对norA1199核苷酸序列的测定揭示了一个编码388个氨基酸的疏水多肽，它与norA编码的蛋白质有95%的同源性。与其他参与转运过程的蛋白质也存在显著同源性，尤其是与四环素外排蛋白以及介导包括氟喹诺酮类在内的结构不相关化合物主动外排的枯草芽孢杆菌Bmr蛋白。在金黄色葡萄球菌中，norA1199编码的蛋白质似乎也作为一种多药外排转运蛋白发挥作用。Southern杂交研究表明，norA1199（或其一个等位基因）是金黄色葡萄球菌的一个天然基因，并且相关序列存在于表皮葡萄球菌基因组中。从SA - 1199B的氟喹诺酮敏感亲本菌株中克隆的norA1199野生型等位基因的核苷酸序列在整个编码区域与norA1199没有差异。Northern（RNA）和Southern杂交研究表明，norA1199转录增加而非基因扩增是SA - 1199B中氟喹诺酮耐药性的基础。
