Centre National de Référence Francisella tularensis, Laboratoire de Bactériologie, Institut de Biologie et de Pathologie, CHU Grenoble Alpes, Grenoble, France; Laboratoire Techniques de l'Ingénierie Médicale et de la Complexité Informatique - Mathématiques et Applications (TIMC-IMAG), Univ. Grenoble Alpes, Centre National de la Recherche Scientifique (CNRS), Grenoble, France.
Technological Advances for Genomics and Clinics (TAGC), Univ. Aix-Marseille II, Marseille, France; Transcriptomic and Genomic Marseille-Luminy (TGML), IBiSA platform, Marseille, France.
Int J Antimicrob Agents. 2020 Dec;56(6):106153. doi: 10.1016/j.ijantimicag.2020.106153. Epub 2020 Sep 8.
Fluoroquinolone (FQ)-resistant mutants were previously selected from the live vaccine strain (LVS) of Francisella tularensis (F. tularensis) subsp. holarctica. This study further characterised all genetic changes that occurred in these mutants during the evolutionary trajectory toward high-level FQ resistance, and their potential impact on F. tularensis antibiotic resistance and intracellular fitness.
The whole genomes of FQ-resistant mutants were determined and compared with those of their parental strain. All detected mutations were evaluated for their potential impact on FQ resistance and intracellular multiplication of F. tularensis.
As compared with the parental LVS genome, 28 mutations were found in the derived FQ-resistant mutants. These mutations involved all genes encoding type II topoisomerases (i.e. gyrA, gyrB, parC, and parE). Interestingly, some of them were not previously associated with FQ resistance, warranting further characterisation. Mutations associated with FQ resistance were also found in other genes, including three encoding proteins involved in transport processes. Most of the detected mutations did not alter multiplication of the corresponding mutants in J774 cells. In contrast, all mutations at locus FTL_0439 encoding FupA/B, a membrane protein involved in iron transport, were associated with FQ resistance and fitness loss.
FQ resistance in F. tularensis is complex and may involve single or combined mutations in genes encoding type II topoisomerases, transport systems and FupA/B. In vivo studies are now required to assess the potential role of these mutations in FQ treatment failures.
先前从土拉弗朗西斯菌（Francisella tularensis）亚种 holarctica 的活疫苗株（LVS）中筛选出氟喹诺酮（FQ）耐药突变体。本研究进一步描述了这些突变体在向高水平 FQ 耐药进化过程中发生的所有遗传变化，及其对土拉弗朗西斯菌抗生素耐药性和细胞内适应性的潜在影响。
确定了 FQ 耐药突变体的全基因组，并将其与亲本菌株的基因组进行比较。评估所有检测到的突变对 FQ 耐药性和土拉弗朗西斯菌细胞内增殖的潜在影响。
与亲本 LVS 基因组相比，衍生的 FQ 耐药突变体中发现了 28 个突变。这些突变涉及所有编码 II 型拓扑异构酶的基因（即 gyrA、gyrB、parC 和 parE）。有趣的是，其中一些突变以前与 FQ 耐药性无关，需要进一步研究。在其他基因中也发现了与 FQ 耐药性相关的突变，包括三个编码参与转运过程的蛋白的基因。大多数检测到的突变并没有改变相应突变体在 J774 细胞中的增殖。相比之下，编码与铁转运有关的膜蛋白 FupA/B 的 FTL_0439 基因座的所有突变都与 FQ 耐药性和适应性丧失有关。
土拉弗朗西斯菌的 FQ 耐药性较为复杂，可能涉及编码 II 型拓扑异构酶、转运系统和 FupA/B 的基因的单个或联合突变。现在需要进行体内研究来评估这些突变在 FQ 治疗失败中的潜在作用。
