Department of Biochemistry, University of Otago, Dunedin, New Zealand.
J Med Microbiol. 2022 Jun;71(6). doi: 10.1099/jmm.0.001551.
Aminoglycoside antibiotics are widely used to treat infections of . The MexXY-OprM efflux pump is an important contributor to aminoglycoside tolerance in reference strains and expression of the genes is repressed by the MexZ repressor protein. Direct investigation of the role of this efflux pump in clinical isolates is relatively limited. The contribution of MexXY-OprM to aminoglycoside resistance is isolate-specific. To quantify the role of MexXY-OprM and its repressor, MexZ, in clinical isolates of The genes were deleted from ten clinical isolates of , and the gene from nine isolates. Antimicrobial susceptibility testing was carried out for commonly used antipseudomonal drugs on the engineered mutants and the isogenic wild-type isolates. RT-qPCR was used to measure expression of the gene. All but one of the mutants were more susceptible to the clinically used aminoglycosides tobramycin, gentamicin and amikacin but the degree to which susceptibility increased varied greatly between isolates. The mutants were also more susceptible to a fluoroquinolone, ciprofloxacin. In three isolates with functional MexZ, deletion of increased expression of and aminoglycoside tolerance. Conversely, deleting from six clinical isolates with sequence variants had little or no effect on expression of or on aminoglycoside susceptibility, consistent with the variants abolishing MexZ function. Genome analysis showed that over 50 % of 619 clinical isolates had sequence variants predicted to reduce the affinity of MexZ for DNA, likely increasing expression and hence efflux of aminoglycosides. Our findings show that the interplay between MexXY, MexZ and the level of expression plays an important role in aminoglycoside resistance in clinical isolates of but the magnitude of the contribution of this efflux pump to resistance is isolate-specific.
氨基糖苷类抗生素被广泛用于治疗 感染。MexXY-OprM 外排泵是 参考菌株中氨基糖苷类药物耐受的重要贡献者，而 基因的表达受到 MexZ 阻遏蛋白的抑制。直接研究该外排泵在临床分离株中的作用相对有限。MexXY-OprM 对 氨基糖苷类药物耐药的贡献具有分离株特异性。为了定量研究 MexXY-OprM 及其阻遏蛋白 MexZ 在 临床分离株中的作用，从 10 株临床分离株中删除了 基因，从 9 株分离株中删除了 基因。对工程突变体和同源野生型分离株进行了常用抗假单胞菌药物的药敏试验。采用 RT-qPCR 测量 基因的表达。除一个外，所有 突变体对临床使用的氨基糖苷类药物妥布霉素、庆大霉素和阿米卡星的敏感性都有所提高，但敏感性增加的程度在分离株之间差异很大。 突变体对氟喹诺酮类药物环丙沙星也更敏感。在 3 个具有功能性 MexZ 的分离株中，删除 增加了 基因的表达和氨基糖苷类药物耐受性。相反，在 6 个具有 序列变异的临床分离株中删除 对 基因的表达或对氨基糖苷类药物的敏感性几乎没有影响，这与变异体破坏 MexZ 功能一致。基因组分析表明，超过 50%的 619 株临床分离株具有预测降低 MexZ 与 DNA 亲和力的序列变异，可能增加 基因的表达并因此增加氨基糖苷类药物的外排。我们的研究结果表明，MexXY、MexZ 和 基因表达水平之间的相互作用在 临床分离株中对氨基糖苷类药物耐药性起着重要作用，但该外排泵对耐药性的贡献程度具有分离株特异性。
