Hauptman-Woodward Medical Research Institute, Buffalo, New York, USA.
mBio. 2012 Aug 31;3(4). doi: 10.1128/mBio.00113-12. Print 2012.
A critical feature of a potential antimicrobial target is the characteristic of being essential for growth and survival during host infection. For bacteria, genome-wide essentiality screens are usually performed on rich laboratory media. This study addressed whether genes detected in that manner were optimal for the identification of antimicrobial targets since the in vivo milieu is fundamentally different. Mutant derivatives of a clinical isolate of Acinetobacter baumannii were screened for growth on human ascites, an ex vivo medium that reflects the infection environment. A subset of 34 mutants with unique gene disruptions that demonstrated little to no growth on ascites underwent evaluation in a rat subcutaneous abscess model, establishing 18 (53%) of these genes as in vivo essential. The putative gene products all had annotated biological functions, represented unrecognized or underexploited antimicrobial targets, and could be grouped into five functional categories: metabolic, two-component signaling systems, DNA/RNA synthesis and regulation, protein transport, and structural. These A. baumannii in vivo essential genes overlapped poorly with the sets of essential genes from other Gram-negative bacteria catalogued in the Database of Essential Genes (DEG), including those of Acinetobacter baylyi, a closely related species. However, this finding was not due to the absence of orthologs. None of the 18 in vivo essential genes identified in this study, or their putative gene products, were targets of FDA-approved drugs or drugs in the developmental pipeline, indicating that a significant portion of the available target space within pathogenic Gram-negative bacteria is currently neglected.
The human pathogen Acinetobacter baumannii is of increasing clinical importance, and a growing proportion of isolates are multiantimicrobial-resistant, pan-antimicrobial-resistant, or extremely resistant strains. This scenario is reflective of the general problem of a critical lack of antimicrobials effective against antimicrobial-resistant Gram-negative bacteria, such as Pseudomonas aeruginosa, Klebsiella pneumoniae, Enterobacter sp., and Escherichia coli. This study identified a set of A. baumannii genes that are essential for growth and survival during infection and demonstrated the importance of using clinically relevant media and in vivo validation while screening for essential genes for the purpose of developing new antimicrobials. Furthermore, it established that if a gene is absent from the Database of Essential Genes, it should not be excluded as a potential antimicrobial target. Lastly, a new set of high-value potential antimicrobial targets for pathogenic Gram-negative bacteria has been identified.
一个潜在抗菌靶点的关键特征是在宿主感染期间对生长和存活至关重要。对于细菌，通常在富含实验室的培养基上进行全基因组必需性筛选。本研究探讨了以这种方式检测到的基因是否是鉴定抗菌靶点的最佳选择，因为体内环境从根本上是不同的。对鲍曼不动杆菌临床分离株的突变体衍生物进行筛选，以在人腹水（一种反映感染环境的体外培养基）上生长。34 个具有独特基因缺失的突变体子集在大鼠皮下脓肿模型中进行了评估，确定其中 18 个（53%）基因在体内是必需的。这些假定的基因产物均具有注释的生物学功能，代表未被识别或利用不足的抗菌靶点，并可分为五个功能类别：代谢、双组分信号系统、DNA/RNA 合成和调控、蛋白质转运和结构。这些鲍曼不动杆菌体内必需基因与数据库中的其他革兰氏阴性菌必需基因（DEG）集重叠很少，包括密切相关的物种鲍氏不动杆菌的必需基因。然而，这一发现并不是由于缺乏同源物。在本研究中鉴定的 18 个体内必需基因或其假定的基因产物都不是 FDA 批准药物或药物开发管道中的药物的靶点，这表明在致病性革兰氏阴性菌中，可用目标空间的很大一部分目前被忽视。
人类病原体鲍曼不动杆菌的临床重要性日益增加，越来越多的分离株对抗多种抗菌药物、泛抗菌药物或极耐药菌株耐药。这种情况反映了普遍缺乏有效对抗抗微生物革兰氏阴性菌（如铜绿假单胞菌、肺炎克雷伯菌、肠杆菌属和大肠杆菌）的抗菌药物的关键问题。本研究确定了一组在感染期间对鲍曼不动杆菌的生长和存活至关重要的基因，并证明了在筛选用于开发新抗菌药物的必需基因时使用临床相关培养基和体内验证的重要性。此外，它还确定了如果一个基因不在必需基因数据库中，就不应该将其排除为潜在的抗菌靶点。最后，确定了一组针对致病性革兰氏阴性菌的新的高价值潜在抗菌靶点。
