Molecular Mechanism of Polymyxin Resistance in Multidrug-Resistant Klebsiella pneumoniae and Escherichia coli Isolates from Henan Province, China: A Multicenter Study.

PURPOSE: To evaluate polymyxin-resistant Klebsiella pneumoniae and Escherichia coli prevalence and characteristics in the Henan province, China. MATERIALS AND METHODS: A total of 2301 bacterial isolates collected at six hospitals were assessed. Their response to polymyxin was evaluated by minimum inhibitory concentration (MIC) analysis, and the mobilized colistin resistance (mcr) and carbapenemase gene were explored. Mutations on mgrB, phoPQ, pmrAB, and crrAB in polymyxin-resistant K. pneumoniae were detected by PCR. phoP, phoQ, pmrK, pmrA, pmrB, and pmrC transcriptional levels were quantified by RT-qPCR. Pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing were performed to determine the phylogenetic relationship between the polymyxin-resistant isolates. RESULTS: Of the E. coli and K. pneumoniae isolates identified, 0.3% and 1.4% were polymyxin-resistant, respectively, with MICs of 4-64 µg/mL. All polymyxin-resistant isolates were susceptible to tigecycline. Four E. coli isolates were mcr-1-positive and one was carbapenem-resistant, carrying bla NDM-5 and mcr-1. One K. pneumoniae isolate was mcr-1-positive and nine were carbapenem-resistant (PRCRKP), carrying bla KPC-2 but not mcr-1. The five E. coli isolates belonged to four sequence types (ST2, ST132, ST632, and ST983). All PRCRKP isolates belonged to ST11. However, all 16 isolates belonged to different PFGE types with <95% genetic similarity. Insertion sequences in mgrB were detected in nine (81.8%) polymyxin-resistant K. pneumoniae samples. Colistin resistance was linked with pmrHFIJKLM operon upregulation, with phoP, phoQ, and pmrK being overexpressed in all but one of the polymyxin-resistant K. pneumoniae samples. Furthermore, 33.3% of patients carrying polymyxin-resistant isolates had previously used polymyxin, and 66.7% patients displayed good clinical outcomes. CONCLUSION: The K. pneumoniae polymyxin resistance rate was slightly higher than that of E. coli and mcr-1 was more common in E. coli than in K. pneumoniae. Moreover, the insertion of ISkpn14 into mgrB may be the main contributor to polymyxin-resistance in K. pneumoniae in Henan.