Copy Number of an Integron-Encoded Antibiotic Resistance Locus Regulates a Virulence and Opacity Switch in Acinetobacter baumannii AB5075.
Copy Number of an Integron-Encoded Antibiotic Resistance Locus Regulates a Virulence and Opacity Switch in Acinetobacter baumannii AB5075.
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DOI：
10.1128/mbio.02338-20
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发表时间：
2020-10-06
期刊：
影响因子：
6.4
通讯作者：
Rather PN
中科院分区：
文献类型：
--
作者：
Anderson SE;Chin CY;Weiss DS;Rather PN
鲍曼不动杆菌仍然是医院获得性感染的主要原因。该物种普遍存在的多重耐药性促使世卫组织将耐碳青霉烯类鲍曼不动杆菌列为研发新抗生素的首要任务。鲍曼不动杆菌的许多菌株经历了高频毒力转换，这是针对这种病原体的新疗法的一个有吸引力的靶点。本研究报道了一种控制菌株AB5075开关频率的新机制。从毒力不透明(VIR-O)变异体到无毒半透明(AV-T)变异体的转换速率受质粒携带的复合整合子上抗生素耐药基因座的拷贝数的正向影响。我们的数据表明，该基因座编码一个调节不透明切换的小RNA。含有该基因单一拷贝的低开关不透明变异体也显示出较低的毒力。这项研究增加了我们对这一关键表型转换的理解，同时也确定了基于毒力的鲍曼不动杆菌治疗的潜在靶点。我们描述了一种新的遗传机制，其中串联扩增质粒携带的整合子通过改变鲍曼不动杆菌AB5075中假定的小RNA(SRNA)的水平来调节毒力、不透明度变异和全球基因表达。该扩增基因座的拷贝数与毒力不透明(VIR-O)和无毒半透明(AV-T)细胞之间的转换率相关。我们发现，典型的VIR-O集落在生长24小时后表现出高水平的切换和与AV-T细胞可见的扇形扇形，其中含有该基因的两个副本。然而，在24小时内没有形成AV-T扇区的不透明集落的子集被发现只有一个拷贝。对AV-T的扇形减少的菌落被指定为低开关不透明(LSO)变体，并且发现相对于VIR-O，开关的开关减少了3个对数。过表达研究表明，调控开关的元件定位于AADB基因的5‘端。Northern blotting表明，该区域编码一个约300nT的 核苷酸(NT)的SRNA，可能负责调节向AV-T的切换。LSO300-ntsRNA的拷贝数也被发现影响毒力，因为∼变异体在小鼠肺部感染期间显示出毒力降低。全球转录图谱显示，>；100基因在VIR-O和Lso变异体之间存在差异表达，这表明∼300-NT sRNA可能作为全球调控因子。一些毒力基因在LSO细胞中表达降低，这可能解释了它们毒力降低的原因。
Acinetobacter baumannii remains a leading cause of hospital-acquired infections. Widespread multidrug resistance in this species has prompted the WHO to name carbapenem-resistant A. baumannii as its top priority for research and development of new antibiotics. Many strains of A. baumannii undergo a high-frequency virulence switch, which is an attractive target for new therapeutics targeting this pathogen. This study reports a novel mechanism controlling the frequency of switching in strain AB5075. The rate of switching from the virulent opaque (VIR-O) to the avirulent translucent (AV-T) variant is positively influenced by the copy number of an antibiotic resistance locus encoded on a plasmid-borne composite integron. Our data suggest that this locus encodes a small RNA that regulates opacity switching. Low-switching opaque variants, which harbor a single copy of this locus, also exhibit decreased virulence. This study increases our understanding of this critical phenotypic switch, while also identifying potential targets for virulence-based A. baumannii treatments. We describe a novel genetic mechanism in which tandem amplification of a plasmid-borne integron regulates virulence, opacity variation, and global gene expression by altering levels of a putative small RNA (sRNA) in Acinetobacter baumannii AB5075. Copy number of this amplified locus correlated with the rate of switching between virulent opaque (VIR-O) and avirulent translucent (AV-T) cells. We found that prototypical VIR-O colonies, which exhibit high levels of switching and visible sectoring with AV-T cells by 24 h of growth, harbor two copies of this locus. However, a subset of opaque colonies that did not form AV-T sectors within 24 h were found to harbor only one copy. The colonies with decreased sectoring to AV-T were designated low-switching opaque (LSO) variants and were found to exhibit a 3-log decrease in switching relative to that of the VIR-O. Overexpression studies revealed that the element regulating switching was localized to the 5′ end of the aadB gene within the amplified locus. Northern blotting indicated that an sRNA of approximately 300 nucleotides (nt) is encoded in this region and is likely responsible for regulating switching to AV-T. Copy number of the ∼300-nt sRNA was also found to affect virulence, as the LSO variant exhibited decreased virulence during murine lung infections. Global transcriptional profiling revealed that >100 genes were differentially expressed between VIR-O and LSO variants, suggesting that the ∼300-nt sRNA may act as a global regulator. Several virulence genes exhibited decreased expression in LSO cells, potentially explaining their decreased virulence.