Schleimer Nina, Kaspar Ursula, Drescher Mike, Seggewiß Jochen, von Eiff Christof, Proctor Richard A, Peters Georg, Kriegeskorte André, Becker Karsten
Institute of Medical Microbiology, University Hospital Münster, Münster, Germany.
Institute of Human Genetics, University Hospital Münster, Münster, Germany.
Front Microbiol. 2018 Aug 14;9:1863. doi: 10.3389/fmicb.2018.01863. eCollection 2018.
Staphylococcal small-colony variants (SCVs) are invasive and persistent due to their ability to thrive intracellularly and to evade the host immune response. Thus, the course of infections due to this phenotype is often chronic, relapsing, and therapy-refractory. In order to improve treatment of patients suffering from SCV-associated infections, it is of major interest to understand triggers for the development of this phenotype, in particular for strains naturally occurring in clinical settings. Within this study, we comprehensively characterized two different triplets each consisting of isogenic strains comprising (i) clinically derived SCV phenotypes with auxotrophy for unsaturated fatty acids, (ii) the corresponding wild-types (WTs), and (iii) spontaneous revertants displaying the normal phenotype (REVs). Comparison of whole genomes revealed that clinical SCV isolates were closely related to their corresponding WTs and REVs showing only seven to eight alterations per genome triplet. However, both SCVs carried a mutation within the energy-coupling factor (ECF) transporter-encoding module (EcfAA'T) resulting in truncated genes. In both cases, these mutations were shown to be naturally restored in the respective REVs. Since ECF transporters are supposed to be essential for optimal bacterial growth, their dysfunction might constitute another mechanism for the formation of naturally occurring SCVs. Another three triplets analyzed revealed neither mutations in the EcfAA'T nor in other FASII-related genes underlining the high diversity of mechanisms leading to the fatty acid-dependent phenotype. This is the first report on the ECF transporter as genetic basis of fatty acid-auxotrophic staphylococcal SCVs.
葡萄球菌小菌落变异株（SCV）具有侵袭性且具有持续性，这是因为它们能够在细胞内茁壮成长并逃避宿主免疫反应。因此，由这种表型引起的感染病程通常是慢性、复发性且难治的。为了改善患有SCV相关感染患者的治疗，了解这种表型产生的触发因素至关重要，尤其是对于临床环境中自然出现的菌株。在本研究中，我们全面表征了两个不同的三联体，每个三联体均由同基因菌株组成，包括（i）临床来源的对不饱和脂肪酸营养缺陷的SCV表型，（ii）相应的野生型（WT），以及（iii）表现出正常表型的自发回复株（REV）。全基因组比较显示，临床SCV分离株与其相应的WT和REV密切相关，每个基因组三联体仅显示七到八个改变。然而，两种SCV在能量偶联因子（ECF）转运蛋白编码模块（EcfAA'T）内均发生了突变，导致基因截短。在这两种情况下，这些突变在各自的REV中均自然恢复。由于ECF转运蛋白被认为对细菌的最佳生长至关重要，其功能障碍可能构成自然产生SCV的另一种机制。分析的另外三个三联体显示，EcfAA'T和其他与II型脂肪酸合成途径（FASII）相关的基因均未发生突变，这突出了导致脂肪酸依赖性表型的机制具有高度多样性。这是关于ECF转运蛋白作为脂肪酸营养缺陷型葡萄球菌SCV遗传基础的首次报道。
