University of Caen Basse-Normandie, EA4655 (team "Antibioresistance"), Medical School, Caen, France.
PLoS Pathog. 2012;8(8):e1002834. doi: 10.1371/journal.ppat.1002834. Epub 2012 Aug 2.
Oxidative stress serves as an important host/environmental signal that triggers a wide range of responses in microorganisms. Here, we identified an oxidative stress sensor and response regulator in the important multidrug-resistant nosocomial pathogen Enterococcus faecium belonging to the MarR family and called AsrR (antibiotic and stress response regulator). The AsrR regulator used cysteine oxidation to sense the hydrogen peroxide which results in its dissociation to promoter DNA. Transcriptome analysis showed that the AsrR regulon was composed of 181 genes, including representing functionally diverse groups involved in pathogenesis, antibiotic and antimicrobial peptide resistance, oxidative stress, and adaptive responses. Consistent with the upregulated expression of the pbp5 gene, encoding a low-affinity penicillin-binding protein, the asrR null mutant was found to be more resistant to β-lactam antibiotics. Deletion of asrR markedly decreased the bactericidal activity of ampicillin and vancomycin, which are both commonly used to treat infections due to enterococci, and also led to over-expression of two major adhesins, acm and ecbA, which resulted in enhanced in vitro adhesion to human intestinal cells. Additional pathogenic traits were also reinforced in the asrR null mutant including greater capacity than the parental strain to form biofilm in vitro and greater persistance in Galleria mellonella colonization and mouse systemic infection models. Despite overexpression of oxidative stress-response genes, deletion of asrR was associated with a decreased oxidative stress resistance in vitro, which correlated with a reduced resistance to phagocytic killing by murine macrophages. Interestingly, both strains showed similar amounts of intracellular reactive oxygen species. Finally, we observed a mutator phenotype and enhanced DNA transfer frequencies in the asrR deleted strain. These data indicate that AsrR plays a major role in antimicrobial resistance and adaptation for survival within the host, thereby contributes importantly to the opportunistic traits of E. faecium.
氧化应激作为一个重要的宿主/环境信号，触发了微生物的广泛反应。在这里，我们在属于 MarR 家族的重要多药耐药医院病原体粪肠球菌中鉴定出一种氧化应激传感器和响应调节剂，并将其命名为 AsrR（抗生素和应激响应调节剂）。AsrR 调节剂利用半胱氨酸氧化来感知过氧化氢，导致其与启动子 DNA 解离。转录组分析表明，AsrR 调控子由 181 个基因组成，包括代表不同功能的基因，涉及发病机制、抗生素和抗菌肽耐药、氧化应激和适应性反应。与 pbp5 基因的上调表达一致，该基因编码一种低亲和力青霉素结合蛋白，asrR 缺失突变体对β-内酰胺类抗生素的耐药性更高。asrR 缺失明显降低了氨苄西林和万古霉素的杀菌活性，这两种抗生素通常用于治疗肠球菌引起的感染，同时也导致了两种主要黏附素 acm 和 ecbA 的过度表达，从而增强了体外与人肠道细胞的黏附。asrR 缺失突变体还增强了其他致病特征，包括比亲本菌株在体外形成生物膜的能力更强，在 Galleria mellonella 定植和小鼠全身感染模型中的持久性更强。尽管氧化应激反应基因的过度表达，asrR 缺失与体外氧化应激抗性降低相关，这与吞噬细胞对其杀伤的抵抗力降低有关。有趣的是，两种菌株的细胞内活性氧水平相似。最后，我们观察到 asrR 缺失菌株表现出突变体表型和增强的 DNA 转移频率。这些数据表明，AsrR 在抗菌耐药性和适应宿主内生存方面发挥着重要作用，从而对粪肠球菌的机会性特征做出了重要贡献。
