ABSTRACT

Polymyxin B (PMB) is increasingly used as a last-line antibiotic; however, the emergence of PMB resistance is a serious threat to global health. Here, a total of 40 Acinetobacter baumannii clinical isolates were collected to screen for PMB-resistant strains. Several clinical isolates including NCCP 16007 were far more resistant to PMB (MIC: 128–256 μg/ml) than the ATCC 17978 strain (MIC: 2 μg/ml) and appeared to possess resistance to broad-spectrum antibiotics including meropenem and 12 others. Four highly PMB-resistant strains possessed point mutations in the histidine kinase PmrB, leading to an increased expression of pmrC encoding a phosphoethanolamine transferase. Whole-genome analyses revealed that the NCCP 16007 stain had acquired two additional copies of the pmrC gene with phage integrase and 13 antibiotic resistance genes (ARGs) from other pathogens, including Klebsiella pneumoniae and Pseudomonas aeruginosa. The GC ratios of the ARGs (50–60%) were higher than that of the chromosomal backbone (39.06%), further supporting the horizontal gene transfer of ARGs. Comparative genomics with other multidrug-resistant A. baumannii strains revealed that the NCCP 16007 strain has many additional ARGs and has lost several virulence factors including Csu pili and heme oxygenase but exhibited high pathogenicity in Galleria mellonella-infection models. The observation of condensed biofilm through confocal and scanning electron microscopy suggested that the NCCP 16007 strain may possess high adhesion capacity during urinary tract infection. Therefore, our genomic and phenotypic analyses suggested that the multidrug-resistant A. baumannii NCCP 16007 strain possesses high genome plasticity, natural transformation ability, and pathogenicity.

摘要

多粘菌素 B (PMB) 越来越多地用作最后的抗生素；然而，PMB耐药性的出现对全球健康构成严重威胁。在这里，共收集了 40株鲍曼不动杆菌临床分离株，用于筛选抗 PMB 菌株。包括 NCCP 16007 在内的几种临床分离株对 PMB（MIC：128–256 μg/ml）的耐药性远高于 ATCC 17978 菌株（MIC：2 μg/ml），并且似乎对包括美罗培南和其他 12 种其他抗生素在内的广谱抗生素具有耐药性. 四个高度抗 PMB 的菌株在组氨酸激酶 PmrB 中具有点突变，导致编码磷酸乙醇胺转移酶的pmrC表达增加。全基因组分析显示 NCCP 16007 染色获得了两个额外的pmrC拷贝具有噬菌体整合酶的基因和来自其他病原体的 13 个抗生素抗性基因 (ARG)，包括肺炎克雷伯菌和铜绿假单胞菌。ARGs的GC比率（50-60%）高于染色体骨架（39.06%），进一步支持了ARGs的水平基因转移。与其他多重耐药鲍曼不动杆菌菌株的比较基因组学显示，NCCP 16007 菌株具有许多额外的 ARG，并失去了包括 Csu pili 和血红素加氧酶在内的几种毒力因子，但在大蜡螟中表现出高致病性- 感染模型。通过共聚焦和扫描电子显微镜观察凝聚的生物膜表明 NCCP 16007 菌株在尿路感染期间可能具有高粘附能力。因此，我们的基因组和表型分析表明，多重耐药鲍曼不动杆菌NCCP 16007 菌株具有高基因组可塑性、自然转化能力和致病性。