Resistance of Klebsiella pneumoniae Strains Carrying blaNDM–1 Gene and the Genetic Environment of blaNDM–1
Tianxin Xiang, Chuanhui Chen, Jiangxiong Wen, Yang Liu, Qí Zhāng, Na Cheng, Xiaoping Wu, Wei Zhang
Abstract
Objective Regional dissemination is the major cause of the widespread prevalence of a plasmid-encoding NDM-1 enzyme. We here investigated the drug resistance, joint efficiency, and gene environment of a Klebsiella pneumoniae strain carrying blaNDM-1. Materials and Methods Carbapenem-insensitive strains were analyzed using the VITEK 2 Compact. Strains carrying blaNDM-1 were identified by polymerase chain reaction and sequencing. Antimicrobial susceptibility testing and plasmid conjugation experiment was then conducted. Strains carrying blaNDM-1 were subjected to Southern blot analysis. After gene mapping of blaNDM-1, library construction and sequencing, plasmids were subsequently spliced and genotyped using the Glimmer 3.0 software and then analyzed by Mauve software. Results Among 1735 carbapenem-insensitive strains, 54 strains of blaNDM-1-positive bacteria were identified, which consist of 44 strains of K. pneumoniae, 8 strains of Acinetobacter baumannii and 2 strains of Escherichia coli. Strains carrying blaNDM-1 had a resistance rate of more than 50% in most antibiotics. Plasmid conjugation between strains carrying blaNDM-1 and E. coli strain J53 had a success rate of 50%. Southern blot analysis indicated that every strain had multiple plasmids containing blaNDM-1. Among the 5 plasmids containing blaNDM-1in K. pneumonia for sequencing, 2 plasmids with complete sequences were obtained. And we found: (i) The p11106 and p12 plasmids were highly similar to pNDM-BTR; (ii) The p11106 and p12 plasmids showed differences in the 20-30 kb region (orf00032-orf00043) from the other six plasmids; and (iii) blaNDM-1 was located in the middle of the orf00032-orf00043 region, where as ble was found nearby. Two tnpA genes were on the top, and orf00052 (tnpA) in the 36kb region was in the downstream sequence. Conclusions A blaNDM-1-containing bacterium exhibits multidrug resistance, which is rapidly spread and transferred by efficient plasmid conjugation. The presence of ble and tnpA suggests that blaNDM-1 originates from A. baumannii, which is retained in K. pneumonia over a long period by transposition of mobile elements. These findings need to be verified by future research.