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Xiaohong Xu,1,* Rongping Zhu,1,* Siyan Lian,1 Hui Zhang,2 Xin Chen,2 Lingfang Fan,1 Peisong Chen,2 Yingping Cao1 1Department of Clinical Laboratory, Fujian Medical University Union Hospital, Fuzhou, Fujian, People’s Republic of China; 2Medical Technology and Engineering, Fujian Medical University, Fuzhou, Fujian, People’s Republic of China*These authors contributed equally to this workCorrespondence: Yingping Cao, Department of Clinical Laboratory, Fujian Medical University Union Hospital, Fuzhou, Fujian, People’s Republic of China, Tel +86-133-6591-0806, Email caoyingping@aliyun.comBackground: The emergence of polymyxin B resistance among carbapenem-resistant Klebsiella pneumoniae (CRKP) causes clinical treatment to be more difficult. We aimed to investigate the risk factors and resistance mechanisms in the polymyxin resistant CRKP (PR-CRKP) strains.Methods: From January 2021 to January 2022, 239 CRKP strains were selected, all of which were analyzed using antimicrobial susceptibility testing and clinical data. Polymerase chain reaction (PCR) was performed for the detection of resistance genes. RT-qPCR was used to quantify transcriptional levels of polymyxin resistance genes. Risk factors for polymyxin B resistant isolates were identified by logistic regression analysis.Results: The resistance rate of polymyxin B was 5.02%. In all CRKP strains, 41.84% came from the ICU. The percentage of carbapenemase producing strains was 93.72%. The main carbapenem resistance gene was blaKPC (90.79%). In the 12 strains of PR-CRKP screened, pmrB and pmrK were overexpressed in all samples which were linked with polymyxin B resistance. Multivariate analysis showed that coronary heart disease may be an independent risk factor predisposing patients to polymyxin B resistance.Conclusion: We determine the multifaceted mechanism and risk factors of polymyxin B resistance in CRKP. Polymyxin resistance is a complex and changing problem, and more research is required.Keywords: polymyxin B resistance, carbapenem-resistantKlebsiella pneumoniae, risk factors, mechanism