摘要

质粒介导的粘菌素抗性基因mcr-1已在世界范围内发现，但含有该基因的生物体的多样性是未知的。在这项研究中，十二个粘菌素耐药的柠檬酸杆菌属。分离物来自中国的病鸡或死鸡，PCR分析表明5个mcr-1阳性。选择具有多药耐药性表型的一种布氏柠檬酸杆菌菌株（SCC4）用于进一步分析。 SCC4对十种测试抗生素具有抗性，对粘菌素的最小抑制浓度（MIC）>4μg/ mL。结合试验证明以每个受体细胞10-7个细胞的频率将粘菌素抗性成功转移至大肠杆菌菌株J53。全基因组测序表明SCC4在其基因组中含有13个抗生素抗性基因，并且mcr-1基因位于最近发现的IncP-1进化枝的44-kb自传型IncP型质粒上。另外，mcr-1基因是插入元件（ISApl1-mcr-1-orf-ISApl1）的一部分，其作为环状中间体形式从质粒中切除。这是动物来源的mcr-1-posiitve C. braakii的第一份报告，我们的研究结果强调了mcr-1可以作为广泛宿主范围质粒的一部分在正常肠道菌群中发现。

The plasmid-mediated colistin resistance gene mcr-1 has been found worldwide, but the diversity of organisms harboring this gene is unknown. In this study, twelve colistin-resistant Citrobacter spp. isolates were obtained from diseased or dead chickens in China, and PCR analysis indicated that five were positive for mcr-1. One Citrobacter braakii strain (SCC4) with a multidrug resistance phenotype was chosen for further analysis. SCC4 was resistant to ten tested antibiotics and the minimum inhibitory concentration (MIC) to colistin was >4 µg/mL. A conjugation assay demonstrated successful transfer of colistin resistance to E. coli strain J53 at a frequency of 10-7 cells per recipient cell. Whole-genome sequencing revealed that SCC4 contains thirteen antibiotic resistance genes in its genome, and the mcr-1 gene resides on a 44-kb self-transmissible IncP-type plasmid of a recently-discovered IncP-1 clade. In addition, themcr-1 gene is part of an insertional element (ISApl1-mcr-1-orf-ISApl1) that was excised from the plasmid as a circular intermediate form. This is the first report of mcr-1-posiitveC. braakii of animal origin and our findings highlight the fact that mcr-1 can be found in normal enteric flora as part of broad-host-range plasmids.

https://www.sciencedirect.com/science/article/pii/S0924857917304739