Epidemiology and Molecular Characteristics of mcr-9 in Citrobacter spp. from Healthy Individuals and Patients in China

Authors：Ju, Xiaoyang; Wang, Siheng; Yang, Xuemei; Han, Weihua; Cai, Chang; Wu, Yuchen; Liu, Congcong; Qian, Jiao; Zhao, Xiaofei; Qian, Xiang; Sun, Qiaoling; Zhang, Rong^*; Chen, Gongxiang^*

Source：Microbiology Spectrum, 2022, 10(6).

DOI：10.1128/spectrum.01346-22

• mcr-9
• Citrobacter spp.
• colistin
• plasmid
• Citrobacter freundii

With the globally prevailing carbapenemase-producing (CP) Citrobacter spp., polymyxin antibiotics have been reconsidered as one of the last-resort treatment options. Our study was conducted to investigate the prevalence of mcr-9 in Citrobacter species. From October to November 2021, 650 fecal samples and 215 Citrobacter isolates were collected from healthy individuals and infected patients, respectively. Isolates were screened for the presence of the mcr-9 gene by the PCR method. mcr-9-carrying strains were identified by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. Due to the susceptibility to colistin, Citrobacter spp. isolates were first induced to increase the expression of mcr-9 on China blue agar plates containing colistin and were then subjected to conjugation experiments. Whole-genome sequencing was performed on the Illumina NovaSeq PE150 system. The prevalence of mcr-9 in the Citrobacter genus from healthy guts and infected patients was 0.62% and 1.86%, respectively. In all mcr-9-positive strains, MICs of polymyxin B were observed at <= 2 mu g/ mL, displaying a nonresistant phenotype. As for conjugation experiments, only one isolate successfully transferred the mcr-9 gene to Escherichia coli C600. Whole-genome sequencing showed that eight mcr-9-positive Citrobacter isolates carried mcr-9 and genes encoding resistance to beta-lactam antibiotics, including bla(CMY), bla(DHA), bla(SHV), bla(TEM), and bla(CTX-M). We also discovered that mcr-9 could be located on the pKPC-CAV1321 plasmid. Our study investigated the prevalence of mcr9 in Citrobacter spp. in both healthy individuals and infected patients and described the carriage of mcr-9 on the pKPC-CAV1321 plasmid for the first time.

• Institution
  1; 浙江大学; 杭州师范大学; 浙江农林大学