Epidemiology and Molecular Characteristics of in spp. from Healthy Individuals and Patients in China.

With the globally prevailing carbapenemase-producing (CP) spp., polymyxin antibiotics have been reconsidered as one of the last-resort treatment options. Our study was conducted to investigate the prevalence of in species. From October to November 2021, 650 fecal samples and 215 isolates were collected from healthy individuals and infected patients, respectively. Isolates were screened for the presence of the gene by the PCR method. -carrying strains were identified by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. Due to the susceptibility to colistin, spp. isolates were first induced to increase the expression of 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 in the genus from healthy guts and infected patients was 0.62% and 1.86%, respectively. In all -positive strains, MICs of polymyxin B were observed at ≤2 μg/mL, displaying a nonresistant phenotype. As for conjugation experiments, only one isolate successfully transferred the gene to Escherichia coli C600. Whole-genome sequencing showed that eight -positive isolates carried and genes encoding resistance to beta-lactam antibiotics, including , , , , and . We also discovered that could be located on the pKPC-CAV1321 plasmid. Our study investigated the prevalence of - in spp. in both healthy individuals and infected patients and described the carriage of on the pKPC-CAV1321 plasmid for the first time. The emergence of homologues posed a serious threat to the therapeutic efficiency of polymyxin antibiotics. Citrobacter freundii is generally regarded as an opportunistic pathogen associated with a variety of nosocomial infections. In this study, we investigated the prevalence of in spp. isolates from healthy individuals and infected patients and highlighted the importance of the rational use of antibiotics. In addition, this epidemiological investigation is the first to describe the carriage of on plasmid pKPC-CAV1321 and confirms the horizontal transfer of this plasmid. Our research may shed new light on further studies of dissemination in humans.