Internal Medicine/Section of Infectious Diseases, Carilion Medical Center and Virginia Tech Carilion School of Medicine, Roanoke, VA, USA; Biomedical Sciences Program, Jefferson College of Health Sciences, Roanoke, VA, USA.
Department of Biochemistry, Virginia Tech, Blacksburg, VA, USA.
J Glob Antimicrob Resist. 2018 Mar;12:79-87. doi: 10.1016/j.jgar.2017.08.017. Epub 2017 Sep 9.
The objectives of this study were (i) to determine the genetic basis for carbapenem resistance in multidrug-resistant (MDR) Acinetobacter baumannii strains isolated from patients affected by a sudden increase in the incidence of infections by such organisms in a tertiary care hospital in Virginia, USA, in 2009-2010 and (ii) to examine whether such strains are commonly encountered in the hospital setting.
The whole genomes of one outbreak strain as well as one carbapenem-resistant and one carbapenem-sensitive strain from sporadic infections in 2010-2012 were sequenced and analysed. Then, 5 outbreak isolates and 57 sporadic isolates (of which 39 were carbapenem-resistant) were screened by PCR for relevant DNA elements identified in the genomics investigation.
All three strains for which whole-genome sequences were obtained carried resistance genes linked to MDR phenotypes and a ca. 111-kbp plasmid (pCMCVTAb1) without drug resistance genes. Of these, the two carbapenem-resistant strains possessed a ca. 74-kbp plasmid (pCMCVTAb2) carrying a Tn2008 transposon that provides high-level carbapenem resistance. PCR analysis showed that all of the outbreak isolates carried both plasmids and Tn2008, and of the sporadic isolates 88% carried pCMCVTAb1, 25% contained pCMCVTAb2 and 50% of the latter group carried Tn2008.
Carbapenem resistance in outbreak strains and 12% of sporadic isolates was due to the pCMCVTAb2-borne Tn2008. This is the first report of a Tn2008-driven outbreak of carbapenem-resistant A. baumannii infections in the Commonwealth of Virginia, which followed similar cases in Pennsylvania and Ohio.
本研究的目的是：(i)确定 2009-2010 年美国弗吉尼亚州一家三级保健医院中多重耐药（MDR）鲍曼不动杆菌感染病例突然增加时，从患者中分离出的耐碳青霉烯类 MDR 鲍曼不动杆菌菌株的遗传基础；(ii) 研究这些菌株是否在医院环境中常见。
对 2010-2012 年散发病例中的 1 株暴发菌株以及 1 株耐碳青霉烯类和 1 株碳青霉烯类敏感株进行全基因组测序和分析。然后，通过 PCR 对基因组研究中鉴定出的相关 DNA 元件，对 5 株暴发分离株和 57 株散发病例分离株（其中 39 株为耐碳青霉烯类）进行筛选。
获得全基因组序列的 3 株菌均携带与 MDR 表型相关的耐药基因和一个约 111kbp 的质粒（pCMCVTAb1），该质粒不携带耐药基因。其中，2 株耐碳青霉烯类菌株携带一个约 74kbp 的质粒（pCMCVTAb2），该质粒携带 Tn2008 转座子，可提供高水平的碳青霉烯类耐药性。PCR 分析显示，所有暴发分离株均携带这两个质粒和 Tn2008，散发病例分离株中 88%携带 pCMCVTAb1，25%含有 pCMCVTAb2，而携带后者的菌株中有 50%携带 Tn2008。
暴发菌株和 12%散发病例的碳青霉烯类耐药性是由 pCMCVTAb2 携带的 Tn2008 引起的。这是弗吉尼亚州首次报告 Tn2008 驱动的碳青霉烯类耐药鲍曼不动杆菌感染暴发，此前宾夕法尼亚州和俄亥俄州也有类似病例报告。
