Objective:To determine the epidemic characteristics of polymyxin resistance ( mcr) genes of Enterobacteriales colonized in patients admitted to hospitals in Zhejiang, Henan, Gansu and Shandong provinces in China in 2023. Methods:A comprehensive collection of 667 fecal specimens from patients admitted to five medical facilities across the provinces of Zhejiang, Henan, Gansu, and Shandong in 2023 was collected. Epidemiological characteristics of Enterobacteriales bacteria positive for the mcr gene were examined, employing techniques such as microbial culturing, using agarose gel electrophoresis, PCR, whole-genome sequencing, bioinformatics analysis, and the induction of antimicrobial resistance. Statistical analysis was subsequently applied to the gathered data. Results:Among 667 fecal samples from admitted patients, five samples were positive for mcr gene, with a carrier rate of 0.75%(5/667), and from two of the samples, two different strains carrying the mcr gene were isolated, respectively. A total of seven strains of Enterobacteriales carrying the mcr gene were detected, of which four strains carried mcr-1 gene and three strains carried mcr-9 gene. The positive isolates included three strains of Escherichia coli, one strain of Citrobacter braakii, Citrobacter freundii, one strain of Klebsiella pneumoniae, and one strain of Enterobacter hormaechei. The seven mcr positive strains were isolated from two distinct geographical locations within China, with four from Zhejiang Province and three from Henan Province. After whole-genome sequencing, it was found that the 16S rRNA sequences of the three strains of mcr-1 positive Escherichia coli had high homology. The three isolates of mcr-9 positive strains preserved a significant degree of homology within the mcr-9 and wbuC regions. Following polymyxin exposure, there was a marked difference in the growth kinetics of the ZJ-307, HN-11-1, and HN-135 strains post-induction compared to their pre-induction growth rates, and their motility capacity was reduced. Conclusions:The prevalence of Enterobacteriales harboring the mcr gene is minimal among hospitalized patients. However, it is noteworthy that these genes are prone to horizontal transfer. They can move into drug-resistant strains, which may have elevate minimum inhibitory concentration(MIC). Resistance to polymyxin can alter the bacterial growth rate and motility, potentially impacting the MIC of other antibiotics, thereby complicating clinical management. Consequently, it is imperative to focus on the proactive screening of susceptible populations to prevent the further dissemination of plasmid-mediated polymyxin resistance among clinically significant gram-negative bacterial pathogens.

Objective:To determine the epidemic characteristics of polymyxin resistance ( mcr) genes of Enterobacteriales colonized in patients admitted to hospitals in Zhejiang, Henan, Gansu and Shandong provinces in China in 2023. Methods:A comprehensive collection of 667 fecal specimens from patients admitted to five medical facilities across the provinces of Zhejiang, Henan, Gansu, and Shandong in 2023 was collected. Epidemiological characteristics of Enterobacteriales bacteria positive for the mcr gene were examined, employing techniques such as microbial culturing, using agarose gel electrophoresis, PCR, whole-genome sequencing, bioinformatics analysis, and the induction of antimicrobial resistance. Statistical analysis was subsequently applied to the gathered data. Results:Among 667 fecal samples from admitted patients, five samples were positive for mcr gene, with a carrier rate of 0.75%(5/667), and from two of the samples, two different strains carrying the mcr gene were isolated, respectively. A total of seven strains of Enterobacteriales carrying the mcr gene were detected, of which four strains carried mcr-1 gene and three strains carried mcr-9 gene. The positive isolates included three strains of Escherichia coli, one strain of Citrobacter braakii, Citrobacter freundii, one strain of Klebsiella pneumoniae, and one strain of Enterobacter hormaechei. The seven mcr positive strains were isolated from two distinct geographical locations within China, with four from Zhejiang Province and three from Henan Province. After whole-genome sequencing, it was found that the 16S rRNA sequences of the three strains of mcr-1 positive Escherichia coli had high homology. The three isolates of mcr-9 positive strains preserved a significant degree of homology within the mcr-9 and wbuC regions. Following polymyxin exposure, there was a marked difference in the growth kinetics of the ZJ-307, HN-11-1, and HN-135 strains post-induction compared to their pre-induction growth rates, and their motility capacity was reduced. Conclusions:The prevalence of Enterobacteriales harboring the mcr gene is minimal among hospitalized patients. However, it is noteworthy that these genes are prone to horizontal transfer. They can move into drug-resistant strains, which may have elevate minimum inhibitory concentration(MIC). Resistance to polymyxin can alter the bacterial growth rate and motility, potentially impacting the MIC of other antibiotics, thereby complicating clinical management. Consequently, it is imperative to focus on the proactive screening of susceptible populations to prevent the further dissemination of plasmid-mediated polymyxin resistance among clinically significant gram-negative bacterial pathogens.