Antimicrobial resistance genes and molecular typing of carbapenem-resis-tant Citrobacter freundii

Abstract:

Objective To analyze the detection rate, distribution characteristics, resistance mechanism, and molecular typing of carbapenem-resistant Citrobacter freundii (CRCF), providing theoretical basis for clinical treatment and prevention. Methods Antimicrobial susceptibility testing results of CRCF isolated from Quanzhou First Hospital Affiliated to Fujian Medical University from 2020 to 2023 were analyzed. Resistance phenotypes of the strains were verified; resistance genes were amplified; strain homology was analyzed by multi-locus sequencing ty-ping (MLST). Whole genome sequencing analysis was performed on CF17 strains carrying both bla_VIM-1 and bla_NDM-1. Results A total of 119 strains of non-repetitive Citrobacter freundii were detected, 27 strains were CRCF, accounting for 22.7%. CRCF was mainly isolated from departments of neurosurgery and urology, and the specimen type was mainly midstream urine. Strains were resistant to both carbapenems and cephalosporins, less resistant to amikacin, susceptible to both tigecycline and polymyxin, and with a resistance rate of >50% to other antimicrobial agents. 22 CRCF strains were successfully recovered and all were positive for antimicrobial resistance phenotype and genes. 17 strains (77.3%) carried single resistance genes, including 14 strains carrying bla_NDM-1, 2 strains carrying bla_KPC-2, and 1 strain carrying bla_NDM-5. 5 strains (22.7%) carried dual antimicrobial resistance genes, including strains carrying both bla_KPC-2 and bla_NDM-1 (n=3), strain carrying both bla_NDM-1 and bla_IMP (n=1), and strain carrying both bla_VIM-1 and bla_NDM-1 (n=1). A total of 8 ST types were detected, with 8 and 6 strains being ST116 and ST532, respectively. CF17 was ST116, carrying bla_VIM-1 and bla_NDM-1 on different plasmids, namely IncA and IncX3, respectively. Conclusion CRCF strains are mostly multidrug-resistant, with the presence of bla_NDM-1 being the major resistance mechanism. Some strains also carry dual resistance genes, mainly ST116 and ST532. CF17 is currently the first isolated and reported Citrobacter freundii that carries both bla_VIM-1 and bla_NDM-1 resistance genes in China.