Multidrug-resistant Citrobacter freundii ST139 co-producing NDM-1 and CMY-152 from China.

The emergence of carbapenemase-producing Citrobacter freundii poses a significant threat to public health worldwide. Here, we reported a C. freundii strain CWH001 which was resistant to all tested antimicrobials except tetracycline. Whole genome sequencing and analysis were performed. The strain, which belonged to a new sequence type ST139, showed close relationship with other foreign C. freundii strains through phylogenetic analysis. A novel variant of the intrinsic bla gene located on the chromosome was identified and designated as bla. Coexistence of bla with qnrS1 was found on a conjugative IncN plasmid, which had a backbone appearing in various plasmids. Other class A ESBL genes (bla and bla) were also detected on two different novel plasmids. The emergence of multidrug-resistant C. freundii is of major concern, causing great challenges to the treatment of clinical infections. Great efforts need to be taken for the specific surveillance of this opportunistic pathogen.