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.
Keywords: polymyxin, Escherichia coli , Klebsiella pneumoniae , mcr , Henan province