Proof of the triple prerequisite conditions which are essential for carbapenem resistance development in Klebsiella pneumoniae by using radiation-mediated mutagenesis.

Evolution of multi-drug resistant bacteria has led to worldwide research to better understand the various resistance mechanisms in these strains. Every year, novel information on carbapenem resistance and its mechanisms is being discovered. In this study, radiation-mediated mutagenesis was used to transform a carbapenem-resistant Klebsiella pneumoniae strain to a carbapenem-susceptible bacterium. Through this process, we proved three conditions of loss of the OmpK35 and the OmpK36 genes and acquisition of blaCMY-10 worked together to produce carbapenem resistance in K. pneumoniae. Loss of only one of the porins did not evoke carbapenem resistance. This is the first report on the essential contribution of these three components of carbapenem resistance in K. pneumoniae.

Resistome Profiles, Plasmid Typing, and Whole-Genome Phylogenetic Tree Analyses of BlaNDM-9 and Mcr-1 Co-Harboring Escherichia coli ST617 from a Patient without a History of Farm Exposure in Korea.

Recently, a blaNDM-9 and mcr-1 co-harboring E. coli ST 617 isolate was identified from an asymptomatic carrier in Korea. An 81-year-old female was admitted to a university hospital for aortic cardiac valve repair surgery. Following surgery, she was admitted to the intensive care unit (ICU) for three days, and carbapenem-resistant E. coli YMC/2017/02/MS631 was isolated from a surveillance culture (rectal swab). Antimicrobial susceptibility testing (AST) for colistin was not performed at that time. Upon retrospective study, further AST revealed resistance to all tested antibiotics, including meropenem, imipenem, ceftazidime-avibactam, amikacin, gentamicin, ciprofloxacin, trimethoprim-sulfamethoxazole, and colistin, with the exception of tigecycline. Whole genome sequencing analyses showed that this strain belonged to the ST617 serotype O89/162: H10 and harbored three ß-lactamase genes (blaTEM-1B, blaCTX-M-55, blaNDM-9), mcr-1, and 14 other resistance genes. Seven plasmid replicon types (IncB, IncFII, IncI2, IncN, IncY, IncR, IncX1) were identified. Horizontal transfer of blaNDM-9 and mcr-1 from donor cells to the recipient E. coli J53 has been observed. blaNDM-9 and mcr-1 were carried by IncB and IncI2 plasmids, respectively. To speculate on the incidence of this strain, routine rectal swab screening to identify asymptomatic carriers might be warranted, in addition to the screening of ICU patients.