Yoon Eun-Jeong, Balloy Viviane, Fiette Laurence, Chignard Michel, Courvalin Patrice, Grillot-Courvalin Catherine
Institut Pasteur, Unité des Agents Antibactériens, Paris, France.
INSERM, UMR S 938, CDR Saint-Antoine, Paris, France Sorbonne Université, UPMC, CDR Saint-Antoine, Paris, France.
mBio. 2016 May 31;7(3):e00697-16. doi: 10.1128/mBio.00697-16.
Overexpression of chromosomal resistance-nodulation-cell division (RND)-type efflux systems with broad substrate specificity contributes to multidrug resistance (MDR) in Acinetobacter baumannii We have shown that modulation of expression of the structural genes for the efflux systems AdeABC and AdeIJK confers MDR and results in numerous alterations of membrane-associated cellular functions, in particular biofilm formation. However, the contribution of these RND pumps to cell fitness and virulence has not yet been studied. The biological cost of an antibiotic resistance mechanism is a key parameter in determining its stability and dissemination. From an entirely sequenced susceptible clinical isolate, we have generated a set of isogenic derivatives having single point mutations resulting in overexpression of each efflux system or with every pump deleted by allelic replacement. We found that overproduction of the pumps results in a significant decrease in fitness of the bacterial host when measured by competition experiments in vitro Fitness and virulence were also evaluated in vivo both in systemic and pulmonary infection models in immunocompetent mice. A diminished competitiveness of the AdeABC-overexpressing mutant was observed only after intraperitoneal inoculation, but not after intranasal inoculation, the latter mimicking the most frequent type of human A. baumannii infection. However, in mice infected intranasally, this mutant was more virulent and stimulated an enhanced neutrophil activation in the lungs. Altogether, these data account for the observation that adeABC overexpression is common in MDR A. baumannii frequently found in ventilator-associated pneumonia.
Overproduction of the RND AdeABC efflux system is observed with a high incidence in multidrug-resistant Acinetobacter baumannii and results in increased resistance to several antibiotics of choice for the treatment of infections caused by this nosocomial pathogen. It was therefore important to study the biological cost of the overexpression of the adeABC structural operon which is normally tightly regulated. Fitness diminution of an overexpressing mutant detected in vitro and in vivo in a model that mimics sepsis was not observed in a pulmonary infection model in which the mutant was more virulent. This points out that increased virulence can occur independently from prolonged persistence in the infected organ and can account for the elevated incidence of this resistance mechanism in clinical isolates. The study also indicates that transposon libraries will identify only virulence genes that are expressed under physiological conditions but not those that are tightly regulated.
具有广泛底物特异性的染色体耐药-固氮-细胞分裂（RND）型外排系统的过表达有助于鲍曼不动杆菌的多药耐药性（MDR）。我们已经表明，外排系统AdeABC和AdeIJK结构基因表达的调节赋予多药耐药性，并导致膜相关细胞功能的大量改变，特别是生物膜形成。然而，这些RND泵对细胞适应性和毒力的贡献尚未得到研究。抗生素耐药机制的生物学代价是决定其稳定性和传播的关键参数。从一个完全测序的敏感临床分离株中，我们产生了一组同基因衍生物，它们具有单点突变，导致每个外排系统过表达或每个泵通过等位基因替换被删除。我们发现，通过体外竞争实验测量，泵的过量产生导致细菌宿主的适应性显著降低。在免疫活性小鼠的全身感染模型和肺部感染模型中也对体内适应性和毒力进行了评估。仅在腹腔接种后观察到AdeABC过表达突变体的竞争力下降，而在鼻内接种后未观察到，后者模拟了人类鲍曼不动杆菌感染最常见的类型。然而，在鼻内感染的小鼠中，该突变体毒性更强，并刺激肺部中性粒细胞活化增强。总之，这些数据解释了在呼吸机相关性肺炎中常见的多药耐药鲍曼不动杆菌中adeABC过表达的现象。
在多药耐药鲍曼不动杆菌中观察到RND AdeABC外排系统的高发生率过表达，导致对几种用于治疗这种医院病原体引起的感染的首选抗生素的耐药性增加。因此，研究通常受到严格调控的adeABC结构操纵子过表达的生物学代价很重要。在模拟败血症的模型中，在体外和体内检测到的过表达突变体的适应性降低在肺部感染模型中未观察到，在该模型中该突变体毒性更强。这表明毒力增加可以独立于在感染器官中的长期存活而发生，并且可以解释该耐药机制在临床分离株中的高发生率。该研究还表明，转座子文库只会鉴定在生理条件下表达的毒力基因，而不会鉴定受到严格调控的基因。
