Infectious Diseases, Novartis Institutes for BioMedical Research, Cambridge, MA 02139, USA.
Antimicrob Agents Chemother. 2009 Dec;53(12):5015-21. doi: 10.1128/AAC.00253-09. Epub 2009 Sep 28.
The intrinsic resistance of P. aeruginosa PAO1 to the peptide deformylase inhibitor (PDF-I) LBM415 was mediated by the MexAB-OprM and MexXY-OprM efflux pumps, the latter of which was strongly induced by LBM415. Single-step exposure of PAO1 deleted for mexAB-oprM (therefore lacking both MexAB-OprM and MexXY-OprM functions) to PDF-Is selected for nfxB mutants, which express the MexCD-OprJ efflux pump, indicating that these compounds are also substrates for this pump. Selection of resistant mutants by use of levels of LBM415 greater than that accommodated by efflux yielded two additional groups of mutations, in the methionyl-tRNA(fmet) formyltransferase (fmt) and folD genes. Both mechanisms are known to impose an in vitro growth deficit (also observed here), presumably due to impairment of protein synthesis. We surmised that this inherent impairment of protein synthesis would upregulate expression of mexXY in a fashion similar to upregulation by LBM415 or by ribosome inhibitory compounds. Transcriptional profiling and/or mexX::lux promoter fusion analysis revealed that fmt and folD mutants were strongly upregulated for mexXY and another gene known to be required for upregulation of the pump, PA5471. Complementation of the fmt mutation in trans reversed this constitutive expression. This supports the notion that MexXY has a natural physiological function responding to impairment of ribosome function or protein synthesis and that fmt mutation (Fmt bypass) and folD mutation generate the intracellular mexXY-inducing signal.
铜绿假单胞菌 PAO1 对肽脱甲酰基酶抑制剂 (PDF-I) LBM415 的固有耐药性是由 MexAB-OprM 和 MexXY-OprM 外排泵介导的，后者被 LBM415 强烈诱导。PAO1 缺失 mexAB-oprM（因此缺乏 MexAB-OprM 和 MexXY-OprM 功能）的一步法暴露于 PDF-Is 中选择了 nfxB 突变体，其表达 MexCD-OprJ 外排泵，表明这些化合物也是该泵的底物。使用大于外排所能容纳的 LBM415 水平选择耐药突变体，产生了 fmt 和 folD 基因中的另外两组突变。两种机制都已知会导致体外生长缺陷（此处也观察到），推测是由于蛋白质合成受损。我们推测，这种蛋白质合成的固有损伤会以类似于 LBM415 或核糖体抑制化合物诱导的方式上调 mexXY 的表达。转录谱分析和/或 mexX::lux 启动子融合分析显示，fmt 和 folD 突变体强烈上调 mexXY 和另一个已知泵上调所需的基因 PA5471。在 trans 中互补 fmt 突变逆转了这种组成型表达。这支持了这样一种观点，即 MexXY 具有响应核糖体功能或蛋白质合成受损的自然生理功能，并且 fmt 突变（Fmt 旁路）和 folD 突变产生细胞内 mexXY 诱导信号。
