Genetic Diversity of Polymyxin-Resistance Mechanisms in Clinical Isolates of Carbapenem-Resistant Klebsiella pneumoniae: a Multicenter Study in China.

Polymyxin has been the last resort to treat multidrug-resistant Klebsiella pneumonia. However, recent studies have revealed that polymyxin-resistant carbapenem-resistant Klebsiella pneumonia (PR-CRKP) emerged due to the mutations in chromosomal genes or the plasmid-harboring gene, leading to lipopolysaccharide modification or efflux of polymyxin through pumps. Further surveillance was required. In the present study we collected PR-CRKP strains from 8 hospitals in 6 provinces/cities across China to identify the carbapenemase and polymyxin resistance genes and epidemiological features by whole-genome sequencing (WGS). The broth microdilution method (BMD) was performed to determine the MIC of polymyxin. Of 662 nonduplicate CRKP strains, 15.26% (101/662) were defined as PR-CRKP; 10 (9.90%) were confirmed as Klebsiella quasipneumoniae by WGS. The strains were further classified into 21 individual sequence types (STs) by using multilocus sequence typing (MLST), with ST11 being prevalent (68/101, 67.33%). Five carbapenemase types were identified among 92 CR-PRKP, (66.67%), (16.83%), (0.99%), (4.95%), and (0.99%). Notably, 2 PR-CRKP strains harbored both and . The inactivation of , associated significantly with high-level polymyxin resistance, was mainly caused by the insertion sequence (IS) insertion (62.96%, 17/27). Furthermore, was inserted coincidently by IS (67/101, 66.33%). The deletion or splicing mutations of were significantly associated with ST11 and KL47 (capsule locus types), and diverse mutations of the gene were identified. Only one strain carried the gene. In summary, the high IS-inserted inactivation, the close relationship between ST11 and the deletion or splicing mutations of the , and the specific features of PR- constituted notable features of our PR-CRKP strains in China. Polymyxin-resistant CRKP is a serious public health threat whose resistance mechanisms should be under continuous surveillance. Here, we collected 662 nonduplicate CRKP strains across China to identify the carbapenemase and polymyxin resistance genes and epidemiological features. Polymyxin resistance mechanism in 101 PR-CRKP strains in China were also investigated, 9.8% of which (10/101) were , as determined via WGS, and inactivation of remained the most crucial polymyxin resistance mechanism, significantly related to high-level resistance. Deletion or splicing mutations of were significantly associated with ST11 and KL47. Diverse mutations of the gene were identified. The plasmid complementation experiment and mRNA expression analysis further confirmed that the promoter and played a critical role in polymyxin resistance. This multicenter study contributed to the understanding of antibiotic resistance forms in China.